In the process of additive manufacturing,due to the control of process parameters,material characteristics and complex shape of the workpiece and othe r factors, the cracks,pores and other defects in the metal workpiece will still occur,whi ch seriously affects the product quality.Therefore,the defect detection of additive manufac turing workpiece is of great significance.In this paper,the research of metal photoac oustic crack detection technology based on optical deflection is carried out.Based on the op tical deflection vibration measurement technology,the verification system of pulse ph otoacoustic crack detection is established,and the corresponding simulation test is carried out.The resolution is better than 20μm,which verifies the feasibility of this technolo gy as a crack detection technology.