Based on long series of measured tidal data and the harmonic analysis method, the long-period variation of the measured tide and astronomical tide downstream of the starting point of tidal bore in Hangzhou Bay were analyzed, and then the influence of astronomical tidal changes on the tidal bore in the Qiantang River was analyzed. The results show that the measured tidal range, tidal arrival time and flood tidal duration of the Zhapu station at the same day and the same tide on 3rd and 18th in lunar August each year vary greatly, with the maximum amplitudes of 1.95 m, 102 min and 122 min, respectively. The maximum variation of tidal range, tidal arrival time and duration of high tide on the same day and the same tide on the 3rd and 18th in lunar August each year at the Zhapu station are 1.52 m, 93 min and 46 min, respectively. The variation of astronomical tide has great influence on the tidal bore. The maximum difference of tidal bore height, arrival time, velocity and steepness of tidal bore at the Yanguan station on the same day and the same tide are 1.12 m, 93 min, 2.05 m/s and 18.1%, respectively.