To remedy the shortcoming of root-mean-square (RMS) error curve method lacking numerical verification, the grey relation method was designed for evaluation of INS/GPS integrated navigation system. Firstly, the theory of grey relation method was introduced; Secondly, Kalman filter was given for INS/GPS integrated navigation system; At last, grey relation was used for filtering performance evaluation in integrated navigation systems, the numerical verification of navigation data before and after filtering was given. The results indicate that filtering performance evaluation in integrated navigation systems based on grey relational is effective, could be used with the method of RMS error curve method.