Abstract: As a typical loess hilly and gully region, the intensity of soil erosion in Yan'an seriously affects the ecological environment security of the region. Based on TM and Landsat images, meteorological data, land use and soil texture data, the dynamic changes and spatial patterns of soil erosion in Yan'an in the 20 years from 2000 to 2020 were quantitatively simulated by using the Revised Universal Soil Loss Equation (RUSLE) and Geodetector model. At the same time, from the ecological service capacity, ecological sensitivity and ecological organizational structure, a comprehensive evaluation system for ecological security was built and an evaluation was conducted. The results show that: (1) The average modulus of soil erosion in 2000 and 2020 were 9 790.40 and 4 249.82 t·km^-2·a^-1, respectively, and the area and intensity of soil erosion showed a double decline trend, and the policy of returning farmland to forest has been effective in the 20 years. However, severe erosion still exists in the eastern part of Zichang County, Yanchuan County and Yanchang County, so the area along the Yellow River basin is currently the priority areas for prevention and governance. (2) The results worked out by geographical detectors show that the main control factors that affect the spatial pattern distribution of soil erosion in the study area is vegetation coverage, followed by the factors of land use type and slope, and the interaction and synergy between vegetation coverage and slope factor is greater than the effect of each single factor on soil erosion. Therefore, the soil erosion area should be comprehensively controlled and prevented by combined consideration on various factors. (3) Compared with the less safe ecological status of Yan'an in 2000, the level of ecological security had been improved to a safe status in 2020. The overall situation of ecological security is showing a trend of overall improvement, partial optimization, but it has not reached to the ideal status of very safe, and the level of ecological security still has a certain potential for improvement. Based on the above research, Yan'an City could be divided into soil erosion control area in the north, water conservation area in the south and the soil erosion sensitive area along the Yellow River, which can provide a scientific basis for soil and water conservation planning and ecological environment construction.

Key words: revised universal soil loss equation, returning farmland to forest, ecological security evaluation, Yan'an City