In order to analyze the characteristics of TPN trajectory, a method of three-dimensional trajectory simulation based on vector operation was designed. The relative movement coordinate was set up in the sight line shifting plane. The relationship between relative movement and sight line shifting was studied. Then vector model of TPN in three-dimensional space was demonstrated, after that vector equation of acceleration was derived consequently. Ship-to-air missile's trajectory was simulated in Matlab when the target was moving in a straight line at a constant speed. The result shows that the model meets the fact, the method works well and that it can express characteristics of trajectory and transformation of every parameter intuitively.