The dosage is an important ingredient of the formation of prescriptions. The dosage of a drug may influences the functions of the dosage of a drug. Increasing or decreasing the dosage of a drug in an established prescription without any change in its ingredients can change its potency or even its compatibility, as well as its action and indication. The discussion of the quantity of the drugs can be in scattered literary datum and the study about dosage still stay at the level of the accumulating of experience, Which affect on the development and inheritance of the science of prescriptions, so it is necessary to arrange the related literary data.This topic research investigated the questions about the dosage from the different aspects: Firstly, this study passes sorting and inducing the related literary data, aims at summing up the theories about dosage in the history of traditional Chinese medicine. Sencondly, it systemically researched modernistic theoretic and experimental studies related to the modification of dosage. Thirdly, it further inquiries into the related problem of dosage quoted from those classic presciptions. Forthly, many compound drugs that consist of no more than 11 drugs were retrieval from the Chinese Formula Database and all the prescriptions which are the same in ingredients while different in the doses were picked out with Access, and were ordered by composition of the prescriptions and divided into groups so as to discuss whether this research method is feasible or not.The effects that the modification of the dosage will exert are many-faceted. This topic basically demonstrated the law of compatibility of prescription on the basis of large amount research and material analysis, providing the important clues andinformations for studying essential question of modification of dosage, offering thoughts and bases for manipulating new prescription of this kinds. The research about modification of dosage is far from the development of the clinical pratice and need be further shrengthened.