Electronic medical records (EMR) application is the development trend of hospital informatization. XML based EMR system is gradually running from the research to the application stage in China. The paper takes XML as the basic storage model, emphatically discusses its design and implementation method. On this basis, it introduces the theoretical basis of adopting XML as the basic storing unit for the electronic medical records, and explores implementation approaches of mutual transformation between relation data model and XML text data model in hospital information systems.