[Objective] To evaluate the value of diffusion weighted magnetic resonance imaging in diagnosis and differential diagnosis of   focal   liver lesions.[Method] Diffusion weighted MR imaging and measurement of apparent diffusion coeffient (ADC value) were performed in 36 normal cases , 98 patients with172 local hepatic lesions( including hepatic cyst 57, hemangioma 39, hepatic carcinoma 32, metastasis 44) .And ADC values were calculated.. The b values were 0, 50, 500. T_1WI、 T2WI was performed in all livers. And multiphase dynamic enchancement was performed in 75 patients to observe dynamic contrast-enchanced change of the lesions.[Result] The average ADC values of focal hepatic lesions with lower b value(0,50) were significantly higher than that with higher b value(0,500). except hepatic cyst . when b=50 s/mm~2, average ADC values of hepatic cyst、 hemangioma、 hepatic carcinoma and metastasis were (3.71±0.30)×10~(-3)mm~2/s、 (7.74±0.74) ×10~(-3)mm~2/s、 (5.16±0.57) ×10~(-3)mm~2/s、 (4.94±0.45) ×10~(-3)mm~2/s. when b=500 s/mm~2, average ADC values of hepatic cyst、 hemangioma、 hepatic carcinoma and metastasis were(3.35±0.31) ×10~(-3)mm~2/s、 (1.72±0.20) ×10~(-3)mm~2/s、 (1.09±0.21) ×10~(-3)mm~2/s、 (1.18±0.14) ×10~(-3)mm~2/s. whether lower or higher b value, the average ADC value of malignant masses(hepatic carcinomas、 metastasis) was significantly different from that of hepatic cysts and hemangiomas(P<0.001). yet, the ADC values of metastatic tumor overlapped with those of hepatic carcinoma. In routine MRI, most of liver masses showed low signal in T_1WI and high or little high signal in T_2WI. In dynamic contrast