The river regime and topographic conditions of Xiangjiaba Hydropower Station downstream are complex，and the fluctuation at the entrance of the approach channel downstream of the ship lift is larger during the flood discharge. Prototype observations show that a wavy water jump is formed in the stilling basin when the surface hole is discharged，and it is transmitted downstream in the form of short waves. Affected by a variety of complex conditions，the longitudinal high-frequency fluctuations of the river under the dam transform into lateral oscillation waves near the entrance area of the approach channel downstream of the ship lift，which has a significant impact on the safety of ship navigation. Analyzing the prototype observation results of the hydraulic fluctuation characteristics of the approach channel entrance area of the downstream approach channel of the Xiangjiaba Junction under different flood discharge flows，we know that the surface flood discharge is the main factor leading to short-wave oscillations in the approach channel entrance area，and its discharge is linearly related to the fluctuation of the entrance area. Moreover，the power station discharge and the middle hole flood discharge have a positive effect on reducing the hydraulic fluctuation in the entrance area.