In order to solve the problem for the non-contact and high precision nondestructive testing of steel-plumbum bonding structures used for radiation inhibition in nuclear industry, the laser ultrasonic testing method was studied. The model of the steel-plumbum bonding structure was established. The propagation of laser ultrasonic and the wave reflection and attenuation induced by the debonding defect were analyzed. The narrowband laser ultrasonic signals were measured at the good bonding and debonding region, and the variation of the amplitude of the interface reflected signal induced by the debonding defect was observed. For the characterization of the debonding defects, the relation of the reflection coefficient with the wave frequency and measuring position was analyzed. The detection and imaging of the specimen with simulated debonding defects were realized by the laser ultrasonic C-scan method. The research results show that the imaging testing of debonding defects in the two-layer steel-plumbum bonding structure can be realized using the laser ultrasonic method, it has application prospect in the nuclear industry for the testing of radiation protection structures.