Abstract: Various kinds of composite materials with simulated defects are prepared as specimen, including the GFRP-Nomex honeycomb sandwich composites, molded composites, and ceramic matrix composites. An air-coupled ultrasonic testing system with dedicated signal processing unit is self-developed and the corresponding experiments are conducted based on the system. The nondestructive testing of the composite specimens with simulated defects are realized, including the detection of disbonding in GFRP-Nomex honeycomb sandwich composites, the testing of delamination in molded composite structures, and the detection of delamination in C/SiC composites. The results prove that the air-coupled ultrasonic testing technology is applicable for the noncontact testing of honeycomb sandwich composites, molded composites, and ceramic matrix composites. It has a wide range of applications in aerospace industry.