Abstract: In inertial navigation system/global navigation satellite system (INS/GNSS) integrated navigation system, the positioning accuracy of integrated navigation solution will be degraded by the outliers of GNSS measurements. The predicted residuals and the setup of adaptive factors are affected if less than four satellites are observed and the satellite geometric distribution is poor. Therefore, a tightly coupled integration algorithm based on robust adaptive extend Kalman filter (EKF) is proposed in this paper. The state transition equation and observation equation of the tightly coupled INS/GNSS system are introduced. The equations of robust equivalent weight factor and adaptive factor constructed by using prediction residual method are derived. In addition, the adaptive factor calculation under the condition of less than four satellites and poor satellite geometric distribution is conducted. The proposed algorithm is verified and analyzed by using land vehicle test data, the experimental results show that the robust adaptive EKF INS/GNSS tightly integration method can effectively reduce the influence caused by satellite outliers. With the proposed algorithm, the navigation accuracy can be further improved under conditions of less than four satellites observable and poor satellite geometric distribution.