The lightning impulse test is carried out on carbon fiber composite laminated board for simulating thunderstroke damage. The transient thermography test method is implemented for detecting the damage defect of different sample, which is a new test method for using the long pulse as a thermal excitation resource. The results of different time is analysed, compared, the outline of the defect is draw, and the size is measured. The research achievement shows that the transient thermography method can detect the delamination defect inside the composite exactly. The transient thermography can differentiate the severity of damage and failure. The measurement result of size and area is correct.