Abstract: During the regular inspection of 30CrMnSiNi2A steel mounting shaft of a certain type of aircraft nose landing gear, it was found that there were many intermittent cracks with different lengths in the circumferential direction of R angle near the end support surface of the suspension shaft. The properties and causes of cracks were analyzed by metallographic analysis, fracture analysis and energy spectrum analysis. The results show that the crack is hydrogen embrittlement cracking, and the microstructure on both sides of the crack is not decarburized; The strength of the mounting shaft meets the requirements, and no metallurgical defects are found. Crack initiation is mainly related to the introduction of hydrogen during surface phosphating treatment and the diffusion of hydrogen caused by high heat treatment strength. It is suggested to optimize the surface treatment process, strengthen the control of hydrogen removal, and adjust the heat treatment parameters to reduce the occurrence of hydrogen embrittlement cracks.