According to the honeycomb sandwich structure of CFRP grid panel and the forming technology and application environment,a test block containing typical defects is designed and made, aiming at effectively detecting the internal debonding, lamination and fiber fracture defects. The detection parameters such as phase-locked period and frequency of lock-in infrared thermography are determined by the test method, and the detection method of lock-in infrared thermography is established. The experimental results show that this method can detect and separate the debonding defects, delamination defects and fiber fracture in the honeycomb sandwich structure of CFRP grid panels.