The P-V integration method based on Kalman filter is usually used on GPS/SINS integrated navigation system. But the attitude, especially azimuth, is not directly observable and then the attitude output by integrated navigation system composed by inertial navigation system with low accuracy is low accurate. Based on the character of vehicle's movement, the GPS azimuth and attitude determined by accelerometers were respectively added in observation at different period. Observation of error angles of platform was improved, convergence rate was faster. Then accuracy of attitude measurement was improved. Simulation results show that the accuracy of attitude measurement using new method is better than the pure P-V integration method.