Abstract: The cause of fracture of SWRCH22A steel self-tapping screw sample during use was explored. Chemical composition analysis, hydrogen content detection, hardness test and metallographic analysis were carried out on the broken screw. The results showed that the chemical composition of the sample met the standard requirements,the hydrogen content met the design requirements, and the surface and core hardness met the technical indicators.But the depth of the carburizing layer exceeds the specified value. Through the in-depth analysis of the fracture morphology of the sample, the local fracture morphology is characterized by intergranular brittle fracture, which is related to improper heat treatment parameters. The screw carburizing process was optimized and improved, and the experiment results were good.