Abstract: The construction of large reservoirs causes water level adjustment downstream of dams, which exerts a significant impact on river regimes, navigation, flood control and ecology. To explore the characteristics of water level variations and their causes in the Hankou—Jiujiang reach of the Middle Yangtze River following the operation of the Three Gorges Dam (TGD), the trend in water level change from 1988 to 2022 was analyzed by the Mann-Kendall analysis method. With the use of the analysis method for the water level amplitude based on the abnormal residual and a one-dimensional hydrodynamic model, in this paper, the contributions of river erosion and silting, downstream control water level and resistance variation to water level change under different discharge levels were estimated. The results showed the following : ① Before the operation of the TGD, the water level at all discharge levels showed nonsignificant changes except for a significant decrease in the low water level (at low discharge levels) at the Jiujiang station. ② After the operation of the TGD, the variation trend in the water level at the Jiujiang station was the same as that before TGD operation. However, the water levels at the Hankou and Huangshigang stations showed significant decreases with decreasing amplitudes of 0.072 and 0.045 m/a and 0.048 and 0.027 m/a, respectively, under discharge levels of 12 000 and 20 000 m³/s, respectively. The critical conversion discharge of water level change was approximately 30 000 m³/s, and there was no obvious water level change near this discharge value. When the discharge was higher than 30 000 m³/s, the water level showed a nonsignificant upward trend, and the increase amplitudes at 45 000 m³/s were 0.037 and 0.049 m/a, respectively. ③ The main reason for the observed water level decrease is river erosion when the discharge is lower than the critical conversion discharge. The main reason why there is no obvious water level change near the critical conversion discharge is that the effect of an increased resistance nearly offsets the influence of river erosion. The main reason for the water level increase is the higher resistance when the discharge exceeds the critical conversion discharge. The obvious increase in the flood water level in individual years is due to the effect of downstream water level jacking.