The paper analyzes problems of patient identity management in the current hospital information system, introduces how the Enterprise Master Patient Index(EMPI) system realizes effective management of patient identity and explains the construction of EMPI from aspects of patient information framework, core algorithm,Patient Indentifier Cross-referencing(PIX) etc. Based on the main index of the inquiry service, registration service and consolidation service, it allows the call by other information systems and provides the indexing service.