The basin upstream the Fulaerji section of the Nenjiang River was selected as the study area. Statistical method and model method were used to evaluate the impact of land use change and the Nierji Reservoir operation on the runoff variation, and the change trend of runoff under the combined influence of the two factors was analyzed. The results show that, the land use change in the basin before and after the construction of the Nierji Reservoir is not obvious, while the runoff change in the downstream is obvious, and the reservoir has a greater impact on the runoff change. SWAT model is suitable for runoff simulation in the study area. The influence of reservoir operation and land use change on the runoff change is 92. 86% and 7. 14% respectively. Under the same rainfall and reservoir operation conditions, the annual runoff can be first decreased and then increased by the land use change from 1990 to 2020, and the reservoir operation has a significant impact on the annual runoff distribution.