A new seamless integrated navigation algorithm was proposed on the basis of ANFIS in order to enhance the performance of GPS/INS integrated navigation system during GPS outages. The algorithm adopted Kalman filter with pseudorange and pseudorange rate observations when the number of GPS satellites was not less 4. Otherwise, ANFIS was used to estimate the navigation errors and restrain the increasing INS errors. Experiments show that the new algorithm can improve the performance of integrated system effectively and enhance the horizontal position accuracy than traditional tight integration algorithms.