In order to explore the influence of the complexity of crack distribution and shape on the particularity of ultrasonic propagation in curved surface components of polymer bonded explosives （PBX）， and optimize the parameters of ultrasonic oblique incidence testing， a numerical model of ultrasonic nondestructive testing of curved PBX components was established， based on the finite element method and typical testing conditions. The surface P under the excitation of transient displacement was calculated and analyzed by COMSOL commercial software. The propagation law of the internal sound field of PBX component was simulated， the ultrasonic detection signals of different angles and cracks were calculated， and the influence of the incident angle and other parameters on the detection results of small angle oblique incidence of ultrasonic water immersion crack of curved PBX component was studied. The numerical simulation results show that when the angle between the beam and the crack is 8°~10°， the small angle oblique incidence ultrasonic detection method has the best detection performance for PBX internal crack defects， and is not affected by the crack depth. At the same time， the curved PBX simulation specimen was designed and manufactured， the small angle ultrasonic testing experiment system was built， and the ultrasonic testing experiments under different incident angles and crack parameters were carried out. The optimal testing angle （8°） obtained from the experiment was consistent with the simulation results （8°~10°）， which verified the rationality of the numerical simulation results and the effectiveness of small angle ultrasonic testing.