Abstract: Metal powders were found in the high pressure oil filter during checking after service for a while. And metal fragments were found in the outside circulation cooling oil filter. It was assumed that the hydraulic pump had worn. After decomposition, it was found that the safety valve of hydraulic pump sleeve had locked, falling off, breaking and wearing had occurred to the spring collar and adjustment collar. The spring collar is made of 60Si2MnA and the adjustment collar is made of 1Cr18Ni10Ti. In this paper, the appearance of the safety valve was observed, and macro and micro observation, microstructure examination and hardness testing were carried out on the broken spring collar and the debris of adjustment collar. The results show that the wear of the hydraulic piston pump was caused by the breakage of the spring collar and the adjustment collar. The failure mode of the spring collar is fatigue fracture, which is related to fretting wear, and the frequent opening of the safety valve might accelerate the fatigue fracture. It is suggested that the abnormal pressure of the oil circuit should be checked, and the filtration performance of the oil filter should be focused on.