The medical service system is an important guarantee for human rights to survival, health and development of every social member, and thus it is significant to explore, interpret and explain the diachronic construction for its legislative reform. In a corpus approach, the study firstly collects the medical-related statutes from 1990 to 2021 in China to build the P.R.C. Medical Legislation Corpus (PRCMLC), and analyzes the keywords and their collocation in the exploratory, explosive and expanding phase of the medical legislative reform. Secondly, from the perspectives of sociosemiotics, the PRCMLC data is combined with the concrete medical laws and regulations for further discussion of the MSS, MIS, DSS and PHS in legislative system. Thirdly, the study explores the core legislative ideas and the relationships among the subsystems in the diachronic analysis, which provide a general overview of the legislative objects, target, participants and mechanisms in the medical reform of China.