The implementation of key projects of conserving soil and water in the upper reaches of the Yangtze River has effectively promoted the control of soil erosion in the Wangjiaqiao small watershed in the Three Gorges Reservoir area. Mann-Kendall test， double cumulative curve method， Chinese Soil Loss Equation（CSLE）， and Geodetector model were comprehensively used to analyze data including the rainfall， runoff， sediment， soil properties， topography， land use， and vegetation coverage collected at the Wangjiaqiao small watershed control station from 1989 to 2021 to clarify the coupling regulation mechanism between erosion “source” and sediment “sink” after implementing the project. The results showed that there was no significant change in the annual rainfall and rainfall erosivity in small watershed in the past 33 years. The annual runoff and sediment yield had a significant downward trend（P<0.01）， with an average annual decrease of 1.46×10? m3 and 493.4 t， respectively， and both experienced sudden changes around 1999. Compared to 1990， the soil erosion modulus in 2020 decreased by 84.3%. The overall intensity of soil erosion in the watershed shifted towards micro-erosion. The sediment yield modulus at the outlet of the watershed decreased by 90.8%， and the sediment delivery ratio decreased from 0.74 to 0.43. The contribution rates of human activities including optimizing land use and improving vegetation coverage to the reduction of slope sediment yield and watershed sediment delivery were 71.3% and 88.7%， respectively. It is indicated that the key projects of preventing and controlling soil and conserving water in the upper reaches of the Yangtze River have achieved sustainable and effective control of sediment at the watershed scale by optimizing the structure of land use and increasing vegetation coverage.