Abstract: The parameter model for low cost tightly-coupled attitude and heading reference system (AHRS)/GPS is established based on fusing pseudo_range-pseudo_range rate-heading measurements. Strong tracking filtering (STF) is introduced to enhance the tracking effect for the highly changeable states of the system owing to the suboptimal parameters. In sequence, due to the large drifts of micro-inertial measurement units (MIMUs), the quadratic EKF (QEKF) approach is proposed, and the quadratic truncation error extracted from the linearization is compensated by computing Hessian matrix. Simulation indicates that STQEKF solution can approach the nonlinear model with high accuracy and rapid, accomplishing navigation control for land vehicles. The control effect for attitude and position is increased by 8.9%~38.2% and 48.7%~54.4% respectively compared with the standard EKF, even if the accuracy of the sensors is modest.