In order to ensure the acquisition performance of GNSS in challenging environment, the problems existing in high dynamic weak signal acquisition are analyzed and a new ins assisted parallel code phase acquisition method is proposed, which uses ins assisted information and satellite ephemeris/almanac to estimate doppler in frequency domain to reduce the frequency search range, and uses code phase estimation and parallel code phase search in code domain to reduce the code phase search time. This method improved the acquisition sensitivity combined with differential coherent accumulation to realize the fast acquisition of high dynamic weak signals. Simulation results showed that the algorithm can significantly improve the acquisition speed and performance of GNSS receiver in high dynamic and weak signal environment.