Trajectory generator is necessary in many inertial navigation research fields. The paper gives the design method of a trajectory generator, and deduces the control equation in detail, then classifies the flight track into four fundamental stages. The trajectory generator resolves the flight track, generates specific force, angular velocity and position signals etc. To check the trajectory generator, the paper designs a navigation solution program. At last, a simulation is demonstrated; the data such as position information generated by trajectory generator and navigation solution equation is compared. Simulation shows that the design is correct and the precision of the trajectory generator is very high.