Abstract: Spacecraft safety is tightly related with structural health status of composite materials. And manufacturing defects have an important influence on the properties of composite materials. It is urgent to study nondestructive testing techniques in the internal structure of composite materials. In this paper, laser ultrasonic technology is provided to test delamination defects in the composite materials. A laser ultrasonic testing system is constructed to detect thickness and delamination defects of composite materials. Finally, depth of defects is located, and the delamination defects of composite materials is reconstructed by the cubic spline interpolation algorithm. The results show that laser ultrasonic testing has advantages of high spatial resolution, measurement accuracy and real-time.