Osteoporosis is a kind of systemic skeletal disease taking bone metabolism obstacles as its performance, the etiology of which is complex, and is not yet completely clear., The high morbidity, high mortality, and high disability rate of osteoporosis have been serious threats to the bone health. With the modern changes in lifestyle and the increasing working pressure, the incidence of osteoporosis tends to be younger, and osteoporosis is no longer the older "patent." Additionally,the incidence of male osteoporosis has significantly increasing trend,and the prevalence of varying degrees of osteoporosis is present for the men whose ages are larger than 65, the most serious complications being fracture and the osteoporosis fracture probability for males greater than that for females. Therefore, it is essential to prevent and treat osteoporosision. Measuring bone mineral density is a reliable method for the early diagnosis of osteoporos and the prediction of osteoporotic fracture. But for osteoporosis diagnostic criteria, at present, there is no complete reunification of the international standards, and the obtained results of different measurement methods also differ. In this study, the best detection method for the bone mineral density in osteoporosis is explored through integratively comparing the various clinical measurements of bone mineral density. Exploring the diagnostic criteria of QCT for osteoporosis, we use quantitative CT (Quantitative Computed Tomography QCT) method to measure the bone mineral densities(bone mineral density BMD) of the last three years (40-79)-years-old middle-aged and old patients in this subject, measuring the volume bone mineral density of its three-dimensional space. dynamic observing the variation of the bone mineral density in osteoporosis in order to achieve the precise determination of BMD, (the clinical value of measurement for the diagnosis of osteoporosis and provide a reliable reference basis), and exploring the incidence of osteoporosis trends in pathogenesis and clinical progress of the latest research means for prevention of osteoporosis and its complications is of great significance.Using United States GE\'s Lightspeed 16-slice spiral row of the CT scanner, the bone densities of the 595 cases (40-79)-year-old middle-aged and old patients in our hospital in the past three years were measured, the lumbar vertebrae 2-4 bone density (BMD) reference values also measured, and the measured values were analyzed and compared with the diagnosis of osteoporosis standard quantitative CT reference value.The subjects studied in our group is the 595 cases (40-79)-years-old middle-aged and old patients in the past three years treated in our hospital, whose average age is 65.5, 298 male cases and 297 female cases. The cases are divided into 4 groups, each case by the 10-years-old. Fractures are presented in a total of 142 patients, 79 men (22 cases of vertebral fractures, 18 cases of femoral neck fractures, 14 cases of radial fractures, 25 cases of hip fracture). 63 women (25 cases of vertebral fractures, femoral neck fractures in 18 cases, seven cases of radial fractures, 13 cases of hip fractures). The patients’bone mineral densities in this group were measured 3-7 days after the fractures or the fracture operations. In addition, male patients were divided into normal group and osteoporosis group to compared with each other, investigating the incidence of osteoporosis for males. The impact of calcium metabolism or bone metabolism in chronic diseases for the patients mentioned above is ruled out, as well as the impact of oral calcium metabolism with the drug and other factors.The 595 cases in this group of elderly patients with bone mineral density (BMD) measured show: the bone mineral densities for both males and females lower gradually after 40 years and the reduction of bone mineral density is more obvious accompanying with the increasing age. The reductions of menopausal women’s bone mineral densities in the age ranges of 50-59 and 60-69 of all ages are apparent due to the changes in hormonal readiness. After 70 years of age the incidences of osteoporoses in men and women are basically the same, but the overall male bone mineral density values are still higher than those of women. By comparing two groups of men we have come to conclude: in the 298 male cases, the bone mineral densities in 226 cases are lower than 113.75mg/cm3, 75.83% of the total. As a result of the existence of unhealthy lifestyles such as smoking and drinking which destroys the male ascendancy in the skeleton aspect with respect to the female, men in the 40-year-old begin to decrease their bone mineral densities, age of onset younger, and the reductions have upward trends with the increasing age. For female,60-65 years-old is a high incidence period for fractures, Males after 70-years-old are in the high rate for fractures.Through determinating the patients’s BMD values in this group, analyzing and comparing the BMD values, the osteoporosis, and the incidence of osteoporotic fracture,we conclude: the male and female bone mineral densities reduced obviously after the age of 40, and the reduction become more clear with the increasin age. The male and female bone mineral densities in the two groups between 50 - 59 years old and 60-69 years old change greatly, especially for the female. This is associated with the hypofunction of female sex hormones and the decline of hormone levels. Early menopause and estrogen lack are likely to result in osteoporosis. Lack of estrogen will lead to the imbalance of the conversion of bone, the ultimate result of which is the osteoclast hypersplenism that makes the bone resorption is more than the bone formation and the bone loss happen. The vast majority of women in about 30 - 35 years of age reach their peak bone mass, and the measurable bone losses begin in 5 - 10 years later. Because of pressure of life, as well as the existence of unhealthy lifestyles such as smoking, drinking, which greatly undermine the male superior postion in terms of bone with respect to the female, male osteoporosis also increased significantly and the incidence of osteoporosis is no longer restricted to postmenopausal women with a high incidence. Alcoholism, sexual dysfunction, the use of corticosteroids and smoking become the four risk factors for the male osteoporosis. Men begin to lose bone mass after 40-year-old, and the diseased population increases year after year. The incidence of 53.24% is present in 40-49 years old, the incidence of 64.06% present in 50-59-year-old, the incidence of 83.54% present in 60-69-year-old,and the incidence of 100% present in 70-79-year-old. There universally exist varying degrees of osteoporoses for men over the age of 65, the most serious complications being the bone fracture. For male, the incidence of fractures become high after 70-year-old,with the osteoporosis fractures occurring mainly in the hip, hip fracture mortality higher than that of women, while women’s fractures usually occur in lumbars, the rates of disability and mortality for male are higher than those of female. Therefore, young people suffering diseases which may reduce peak bone mass or accelerate bone loss, the postmenopausal women with diseases clearly increasing the risk of fractures,and the older men should be measured BMD, which plays an essential role in the detection of osteoporosis and prevention.Among the bone mineral density measurement approaches, the QCT method has an irreplaceable advantage, that is, the QCT technology is safe, reliable,and of easy operation. QCT is one kind of osteoporosis changing techniques that observes the bone mineral density dynamically, and QCT can be a separate determination of a high metabolic rate of cancellous bone mineral content and thus improve the sensitivity of observed changes in BMD. It measures the volume bone mineral density of the three-dimensional space and the results of its determinations are of high repeatability, the measured bone mineral densities being of high sensitivity, accuracy,and repeatability. QCT has the stability in determination of cancellous bone , which can shorten the observation period, in favor of short-term observation follow-up after treatment, contribute to dynamic understanding of the healing efficacy, and accordingly guiding the adjustments clinical treatments. It has the irreplaceable advantages in comprison with the other screening devices. In clinical applications, it has shown favorable development prospects.