Taking the outpatient information of large comprehensive children hospitals in Chongqing as data sources, the paper conducts data preprocessing with SQL Server 2008 R2, uses the technology of association rule to excavate the rule of association between the symptoms and signs and the registered departments. It provides a decision-making basis for outpatients to select the department to be registered and lays a foundation for subsequent research and development of the self-help department diversion system for outpatients.