Abstract: A nondestructive testing system was constructed based on the principle of laser shear speckle interferometry. The influences of negative pressure loading rate and image spatial resolution on the effective recognition rate of debonding defects in the automatic detection of coated propellant grains were investigated. Finite element simulation was adopted to analyze the identifiable threshold of the out-of-plane displacement derivative of defects, and the variation trend of the measured size of debonding defects with out-of-plane displacement was clarified. The results show that the recognition rate of the system for debonding defects is significantly improved with the reduction of negative pressure loading rate and the increase of image spatial resolution. The detected size of defects presents an increasing trend as the threshold of out-of-plane displacement derivative decreases and the out-of-plane displacement rises. The detection threshold of out-of-plane displacement derivative of the constructed testing system is approximately 60×10⁻⁶. Under this threshold, when the out-of-plane displacement of a defect with a diameter of 10 mm is about 0.4 μm, the detected size of the defect is approximately equal to its actual size.