Abstract: In order to improve the tracking performance of global positioning system (GPS) in high dynamic environment and provide reliable calibration information for strapdown inertial navigation system (SINS), the scheme of SINS aiding GPS ultratightly coupled navigation was presented. Considering  the poor tracking performance of the carrier phase lock loop (PLL) in high dynamic applications, Doppler frequency derived from SINS parameters was provided for PLL, and so the effect of vehicle dynamics on PLL was decreased. Additionally, in order to eliminate the measurement correlation caused by introducing SINS aiding information, the relationships between PLL errors and SINS errors have been established and PLL errors were appended to the system state vector. Finally, the simulations indicate the ultra-tightly coupled system can not only enhance the antijamming capability and the dynamic tracking performance of the tracking loops effectively, but also improve the error estimating precision of the integrated Kalman filter significantly.