Abstract: Several cracks with different lengths were found on the surface of 20SiMn2MoVA steel high strength bolt when magnetic particle inspection. Macroscopic analysis, mechanical properties test, chemical composition analysis and metallographic examination were used to analyze the causes of cracks. The results show that the cracks on the surface of the high strength bolt belonged to forging folding defect. In the forging process, the uneven forging process and deformation caused the forging streamline to be blocked and the edge fin to be formed, which eventually led to the formation of forging folding defects.