[Objective] The spatiotemporal changes of different grades of sloping farmland, the soil conservation effects of different sloping farmland types, and the impact of returning farmland to forest or grassland on sloping farmland and soil conservation at the source area of Weihe River were studied in order to provide a scientific basis for the rational planning and utilization of different sloping farmland resources. [Methods] Land use and topographic data at the source area of Weihe River from 1990 to 2020 were analyzed by superposition analysis, farmland dynamic attitude, land use transfer matrix, and the Chinese soil loss equation. [Results] ① During 1990 to 2020, the area of cultivated land increased slowly, then decreased sharply, and then decreased slowly, with a net decrease of 321.03 km². Steep slope cultivated land and gentle slope cultivated land were the main types of cultivated land change. ② The temporal and spatial changes of cultivated land were mainly characterized by a small increase in cultivated land from 1990 to 2000, mainly located in Zhangxian County and Minxian County. With the implementation of the grain for green project (GGP), 279.80 km² of sloping land were transformed into forest and grassland, in which the conversion of cultivated land to grassland was mainly located in Tongwei and Longxi counties, while the conversion of cultivated land to forest land was mainly located in Longxi and Minxian counties. ③ The reclamation of forest and grassland at the source area of Weihe River from 1990 to 2000 reduced soil conservation by 5.52×10⁴ t, while returning farmland to forest and grassland increased soil conservation by 2.21×10⁶ t from 2000 to 2020. The transformation of sloping land with greater than 15° slope could affect changes in soil conservation. [Conclusion] The implementation of GGP has achieved remarkable results at the source area of Weihe River. The area of farmland conversion on steep slopes was the largest from 2000 to 2010. The soil conservation effect on steep slopes was the largest on abandoned land. Steeply sloping farmland will be the main target during the new round of returning farmland.