Abstract: A 303Se stainless steel high lock nut cracked along the axis direction. The causes of cracking were analyzed by metallographic examination, hardness test, scanning electron microscope analysis and residual stress test. The results show that the tensile strength of 303Se stainless steel increased and the plasticity decreased during cold extrusion, so the radial bearing capacity of 303Se stainless steel became worse and cracking occured under high load. The product process optimization could effectively improve the radial bearing capacity of stainless steel high lock nut.