The paper introduces the definition of precision medicine and its new medical models, points out that the Clinical Decision Support System(CDSS) is the core step for the realization of precision medicine. In the development of precision medicine, medical informatics should play a key role in guiding the research directions, guaranteeing the accuracy and repeatability of knowledge, changing the timeliness of knowledge transmission and building the knowledge review mechanism, etc. Besides, it explains key missions for medical informatics in promoting the development of precision medicine.