Composite material is fourth largest aviation materials after the aluminum, steel, titanium and has been widely used in aviation. Defects and damages is inevitable in the process of its production and manufacturing, that seriously hazards the aviation security. Tap testing is the simplest and the most widely used nondestructive testing (NDT) method, but it encountered many problems developing in the direction of intelligent. In this paper, the composite material structural characteristics, defects and damages, security, knock detection principle, knock hammer design, signal processing unit, database building and intelligent detection algorithm were further studied, and the knock detection standard process and specification, database construction methods and intelligent clustering... algorithm was put forward. Finally, the intelligent tap testing system is developed based on above research.