Abstract: The microstructure of martensitic stainless steel with cracks produced during shearing was investigated by means of chemical composition analysis,optical microscope,scanning electron microscopy and energy spectrometer. The results showed that the microstructure was mainly made up of ferrite matrix,δ ferrite phase and carbides,and the carbides were mainly distributed on the grain boundary as reticulation and phase boundary as chain. Based on the test results and the deformation characterization of the steel in shearing,the mechanism of shearing cracking was explained,and suggestions was given to resolve the problem.