Medical and health big data is an important basic strategic resource of the country and an important asset of medical and health institutions. In the face of medical and health informatization, the paper analyzes the status quo of research and application at home and abroad, discusses the main sources and characteristics of medical and health big data, and the opportunities and challenges, puts forward related issues. It also discusses the content management, data security, data quality, master data management, data sharing and other issues and their countermeasures of medical and health data governance for the better practical application of medical and health big data.