Over the past 70 years, the water diversion at the three outlets of the Jingjiang River has been continuously decreasing. In order to investigate the driving factors at different historical stages, this study used the measured hydrological data of the hydrology and topographic features of the mainstream and tributaries from 1955 to 2021, and identified the contributions of the factors based on the variable control approach. The results showed that the water diversion had gradually decreased, and the decrease had mainly occurred from May to November. The decrease in water diversion was greatly aggravated by the reduced mainstream inflow due to the decrease in precipitation in the upper Yangtze, and the erosion of the mainstream bed and deposition at the three outlets caused by the dam projects in the lower Jingjiang River and the sediment trap in the Gezhouba. However, the Tiaoxiankou dam had little effect on water diversion. Since the damming of the Three Gorges Reservoir (TGR), the mainstream and the three tributaries had experienced synchronous riverbed erosion, resulting in an imperceptible change in water diversion. The reduction in rainfall had been concentrated in the rainy season, which had had a major impact on the reduction in water diversion from May to November. Meanwhile, water diversion was mainly concentrated in the rainy season when the mainstream was at flood level, resulting in a large decrease in water diversion from May to November, while the Lower Jingjiang Cutoff Projects triggered a large lowering of the mainstream riverbed. In addition, the operation of Gezhouba, the initial damming of TGR and the experimental damming of TGR were mainly carried out from May to November, reducing water diversion by 0.4×10⁸ m³, 12.5×10⁸ m³ and 38.6×10⁸ m³, respectively. The enabling effect of the Tiaoxiaokou dam on water diversion was far less than the constraining effect of rainfall reduction, resulting in a negative contribution ratio for the dam. In comparison, the contribution ratio of the lower Jingjiang dam projects reached 85%. In the post-dam period, precipitation dominated water diversion reduction with a contribution ratio of more than 50%, while Gezhouba operation hardly played a role and its downstream riverbed adjustment produced a contribution ratio of 21%. During the initial and experimental damming of the TGR, the contribution ratios of its operation increased to 7% and 23%, respectively, while those of its downstream riverbed adjustment were 10% and 19%. As the precipitation decline in the upper Yangtze will continue at least until the end of this century, the annual water diversion will show a long-term downward trend, while the water diversion at a given mainstream flow will change little due to synchronous riverbed erosion between the mainstream and the three outlets.