Abstract: Aimed at the particularity of stock ammunition safety,points out the demerits of traditional probability calculate methods such as ETA and FTA on the basis of enumerating the domestic and overseas stock ammunition accident cases.Puts forwards a probability calculation method of stock ammunition accident based on FID,and describes the procedure and arithmetic of FID model.Finally,with the ammunition-stolen accident as an example,the accident probability distribution chart and accumulation probability curve are calculated and obtained.The result shows that the procedure and arithmetic of FID model can overcome the demerits of ETA and FTA methods.Analysis result also shows that the tiptop subjection degree of ammunition-stolen accident is 10~(-4),and accident probability tends to be 10~(-3) to 10~(-1),thus it is concluded that if the safety measure could not achieve the standard,the ammunition-stolen accident will stand a good chance to happen.