Due to land use change and reservoir operation, the flood process has been greatly affected in the upper reaches of the Ganjiang River Basin since the 1980s. It is of great significance to analyze the influence of land use change and reservoir operation on the flood process in the upper reaches of the Ganjiang River. Taking the Pingjiang River Basin in the upper reaches of the Ganjiang River as an example, based on different underlying surface conditions, this study divided the watershed land use from 1981 to 2021 into 1981-1992, 2000-2010 and 2011-2021, recorded as 85 period, 05 period, and 20 period, respectively, used scenario analysis to create land use and reservoir operation scenarios for these three periods. The flood process was simulated using MIKE SHE under various scenarios, effects of land use change and reservoir operation on flood peak, flood volume, and peak time were further analyzed. Results showed that from 1985 to 2020, the proportion of grassland and cultivated land decreased by 3.49% and 1.72%, respectively, while forest land and construction land increased by 3.98% and 1.41% in proportion, respectively. Under such condition, the flood peak and volume for 2020 decreased by 6.14% and 7.03%, respectively, compared with those for 1985, and the peak time was delayed by 1.5 h, which accounted for 48%, 50%, and 51% of the effects of the changes in the underlying surface. Due to the effect of reservoir operation on the flood process, the flood peak and volume decreased by 6.60% and 5.72%, respectively, while the peak time increased by 12.29%, contributing to 52%, 50% and 49% of the changes in the flood peak, flood volume and peak time, respectively. Furthermore, the results showed that the flood peak and volume were reduced to a certain extent due to land use change, but the delay degree of peak time was different. The effects of major and medium flood events were lower than those of minor flood events, which related to the land use cover machanism of land expansion and vegetation cover growth. Under the influence of reservoir operation, the peak and volume of major flood events were more sensitive than those of medium flood events, whereas those of minor flood events were relatively insensitive, and the peak time of these flood events was delayed. This study analyzed the impact of reservoir operation and land use change on the flood process, which can provide a scientific basis for watershed flood forecasting.