The basic concept of killing zone is presented, which can be divided into the vertical killing zone and the horizontal one. Considering that the missile speed vector can be decomposed into the vertical plane and the horizontal plane, the three-dimensional method of proportional guidance trajectory is introduced, which is then used to simulate the process of missile/target encountering under the guidance of single warship and dual-warship cooperation. The simulation results show that collaborative guidance can greatly improve the far edge of the killing zone of the ship-to-air missile at low altitude, and effectively improve the operational efficiency of the missile.