Abstract: Some 30CrMnSiA firing pins were found to have cracks at the surface after heat treatment.In order to find out the cracking cause of the firing pins,macro and micro observation on the fracture surface,energy spectrum analysis,metallurgical structure examination and micro-hardness testing were carried out and the results were compared with the test results of raw material.The results show that there are original defects (fold) in raw material,which is the main cause for the cracking of the firing pins.It is proposed that nondestructive inspection should be used before heat treatment of raw material in order to get rid of the possible existence of original defects (fold).