Abstract: Oil leakage occurs easily in the application of compressor, which can cause serious consequences. The bearing seat of a compressor is connected with the shell by pin and then the both are welded to gether. Oil leakage was found at the welding position during its use. In order to identify the reason to provide reference for related fault processing, nondestructive test, microstructure and microhardness test were carried out for the oil leakage position. The results show that the welding hot crack formed during welding process is the cause of compressor oil leakage.