Abstract: During the process of ground routine inspection of a certain type plane, the LY12 corner plate which used to fix the hydraulic pipe was found to be fractured. After this incident, some corner plates of the same material and the same heat treatment which used to fix the hydraulic pipe on the other position were also found to be fractured. In this paper, macro-morphology and micro-morphology observation, composition analysis, metallurgical structure examination, micro hardness test of the failure corner plate were all carried out to analyze the failure reasons of the failure corner, and the actual installation of the corner plate was also be checked. The results show that the fracture property of the corner plate is fatigue fracture, which is the comprehensive result of actual assembly structure and force action. According to the analysis result, the improvement measures and suggestions such as adding additional fixtures or replacing the material of corner plate are put forward.