Abstract: This paper mainly describes that Rod Cluster Control Assembly of nuclear power plant may produce three main type of defects during operation, such as wear, swell and crack. These defects may make a great hidden danger to reactor safety operation or in severe cases may even cause the reactor fail to stop, so resulting to nuclear safety accidents. Combining the inspection technology of the automatic ultrasonic and eddy current examination can effectively detect the main defects of Rod Cluster Control Assembly. This paper mainly expounds the causes and mechanism of main defects in Rod Cluster Control Assembly together with ultrasonic and eddy current examination technology principle and method, and summarizes the characteristics of the typical defects during onsite implementing inspection and analysis methods of defect signal.