Abstract: In view of the problem of crack defects on the surface of 310S stainless steel medium thickness plate, the macrostructure test and surface penetration test were carried out on the continuous casting slab, and then the scanning electron microscope analysis and metallographic examination were carried out on the hot rolled steel plate with crack defects. The results show that the hot rolled steel plate was obviously divided into recrystallization and non-recrystallization regions, and the cracks were all located in the recrystallization region. Due to the difference of deformation resistance between recrystallization and non-recrystallization regions, during the rolling process of steel plate, cracks began to appear with weak deformation resistance area and extend to the surface of steel plate, which was the main reason for surface crack defects.