To accurately describe the killing effect of missiles especially dealing with the small or fast target, a new method for calculating the killing effect of missiles is proposed in this paper. The missile and the target are divided into several basic geometries based on their shapes, and then the equations of these geometries are established in their local frame. The mass center motion equations of the target and the missile are determined in the light of their initial positions and velocities, respectively, and every geometry moves with its center of mass according to its attitude. The equations of the fuze view field and the target can confirm whether the fuze detects the target, and whether the fragment hit the target can be certified by the same approach. This paper also writes a MATLAB simulation program for this calculation method and designs a new algorithm to determine the position relationship of space geometry using existing functions, and the simulation verifies the effectiveness of this method.