Missile-infosystem is core of a weapon system; its safety is more and more important. In this paper, based on the concept of safety, a method to ensure safety was offered. The method, which is based on classification of safety, is a mixture of instruction protection, enhancing the coverage scale-self-check, range discretion, SoC, ROM interference. This method has been already applied in our project. The safety of products is improved. In this way, combination property of the weapon system is enhanced.