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Since the end of the 1990s, large-scale ecological restoration projects have been implemented in the Loess Plateau, which significantly changed land use types and land cover. These projects enhanced ecosystem service functions and improved soil and water loss to a certain extent. More and more attention has been paid to the impact of these projects on the hydrological processes. The Yanhe River Basin, with a semihumid climate in the middle of the Loess Plateau, was taken as an example. The community land model (CLM) version 5.0 was used to simulate the impact of land cover changes on key hydrological elements and their relationships in this basin over 1980 through 2018. The results showed that the cultivated area was decreased from 3277km2 in 1980 to 2400km2 in 2018, a decrease of 26.76%. Woodland and grassland area was increased by 244km2 and 528km2, respectively. The annual runoff and annual runoff coefficient was decreased significantly due to the change of land cover, which were 12.34% and 11.46%, respectively. The change of land cover also led to the decrease of monthly mean runoff and the coefficient, which had a less influence in the wet season and a larger influence in the dry season, making the annual runoff distribution to be centralized. To guide the rational use of the water resource and build a harmonious ecological environment in the Loess Plateau, understanding the hydrological process and its changing had a great theoretical value and practical significance.