Abstract: By analyzing the gain matrix,we find that the general index for verifying the accuracy of the attitude parameter is not reasonable on maneuver condition because the attitude estimators,and their update covariance matrix are influenced by inaccurate predictors in classical Kalman filtering.A new verifying idea according to some components of the velocity vector in body frame equal zero in the GPS/INS system is proposed.The new method need not add the additional sensors,so it is economical,convenient and simple.