Abstract: In current research into integrated navigation based on geomagnetic information, the nonlinear process caused by the multi-sample algorithm causes filter precision to decline sharply. To solve this problem, we propose an algorithm of tri-sample attitude determination. The algorithm uses the system error equation as its state equation and employs a linear Kalman filter to deal with geomagnetic information. The attitude is obtained by correcting the output with the estimated attitude error. Simulation is conducted on the SINS/geomagnetic integrated navigation system, and the results are compared with those of the tri-sample algorithm. The simulation results show that our algorithm can track the attitude variation and restrain the error divergence effectively.