Online medical diagnosis is becoming more and more popular, so more and more data are in electronic records.How to reduce the redundancy of medical data, extract useful medical value rapidly from a large number of medical data, and improve the speed and accuracy of medical diagnosis has become a hot issue.In view of it, some data of diagnosis of lung cancer in medical system are researched,and the C4.5 algorithm of attribute reduction based on attribute-dependent improved discernibility matrix is establishe...