In order to research influence of the interaction between the terminal guided projectile and the inertial guided gyro on trajectory, firstly, the configuration was introduced, the mechanical relationship between them was analyzed with Newton-Euler; Secondly, the mathematical model of the terminal guided projectile was set up. The Matlab/Simulink software was used for the procedure, and calculation of this mathematical model was carried out. Eventually, the difference between sole-body and multi-body model was contrasted, the influence of inertial guided gyro's configuration parameter on trajectory was analyzed. The results indicate that multi-body model accurately describe the law in the motion of the terminal guide projectile. A foundation for compiling terminal guide projectile's range table and enhancing precision of the terminal guide projectile's trajectory was laid.