Abstract: Referring to the object of high precision fiber optic gyro (FOG) strapdown inertial navigation system, the overall system design method based on the simulation is put forward. The key technology of FOG strapdown system design is analyzed. The design of body movement trajectory , the choose rule of Kalman filter variable state , the management of external assistant information and the application of Kalman filter in the initial ground alignment are emphasized to study. The simulation example of different filter variable state, the different integrated navigation time, one position ground alignment and two position ground alignment are compared. The result indicates that the topic of the system design is Kalman filter which ties up the dynamic characteristic, the integrated navigation mode and the inertial instrument accuracy level.