Abstract: The paper studies the method and area of application of data mining in enterprises, analyzes the necessity of classification for finance customers, and introduces the method of customer classification. A decision tree algorithm is developed based on the ID3 algorithm and applied it to a real project. A two layer software structure for the visualization of classification data mining is used in the project. The method has been applied in a banking CRM system. User's response is positive, and it has helped a lot to the enterprise in decision support areas.