Abstract: In order to advance tight integrated navigation precision and stability of fiber optic gyroscope (FOG) strap-down inertial navigation system(SINS) and globe navigation satellite system(GNSS), a SINS/ GNSS tight integrated navigation system was designed based on pseudo range and pseudo range rate. For the white Gaussian noise of FOG and instability of error statistics and model, the residual error was calculated in the evaluation of error variance matrix, an improved adaptive Kalman filtering method was proposed. Optimal estimation of navigation parameters were obtained with the improved adaptive Kalman filtering method, and system was corrected with feedback compensation. Then the divergence of Kalman filtering was well restrained and the stability of the system was enhanced. Through the static test, the results demonstrate that the designed fiber optic gyroscope SINS/GNSS system has good robustness. Under the condition of three navigation satellites, system could maintain nice navigation accuracy that verifies the excellence of tight integrated navigation.