Exploring the mechanism of landscape pattern changes on soil erosion can provide a scientific basis for the prevention and control of soil and water loss and the maintenance of regional ecological security. Based on the land use data of 2000, 2010, and 2020, this paper systematically revealed the changes in landscape patterns and their impact on soil erosion in the Southwest Alpine Canyon Area of China by using the methods of landscape pattern index, RUSLE model, and geographical detector. The main conclusions were as follows: (1) Woodland and grassland were the dominant landscape types in the Southwest Alpine Canyon Area of China, and their average area accounted for 45.82% and 40.22% respectively, but their dominant position was weakening; From 2000 to 2020, the landscape pattern of the study area has changed significantly, mainly manifested by the expansion of cultivated land (+1609.49 km²), the reduction of forest land (-2697.10 km²), and the rapid degradation of grassland (-40458.68 km²). (2) The landscape structure presented a compound evolution characteristic of "increased diversity-decreased connectivity-intensified fragmentation", especially the trend of fragmentation from 2010 to 2020 was more apparent. Different land categories showed distinct differentiation rules: the integrity of the forest landscape further strengthened, the number of patches (NP) and patch density (PD) decreased by 23.18% and 18.18% respectively; the degree of grassland fragmentation intensifies, and the largest patch index (LPI) decreased by 10.74%; the spatial agglomeration feature of construction land was particularly prominent. (3) Soil erosion was mainly moderate and mild, accounting for more than 80% in total. However, the overall situation of soil erosion was worsening, with the area of severe erosion increasing by 931.94 km². Spatially, the intensity of soil erosion presented a pattern of being higher in the southeast and lower in the northwest, with localized concentrations. The water storage and soil conservation area in the high mountain canyons of northern Yunnan-southwestern Sichuan, and the ecological maintenance area in the high mountain canyons of northwestern Yunnan constituted high-incidence areas for soil erosion. The proportions of areas with intense and above levels of soil erosion in these regions were 33.49% and 21.52%, respectively, of the total areas with the same level of soil erosion in the study area. (4) At the patch level, the Largest Patch Index (LPI) was the main factor affecting soil erosion in farmland and grassland, while the Patch Cohesion (COHESION) was the key indicator explaining the variation in forest soil erosion. At the landscape level, the Splitting Index (SPLIT), Landscape Shape Index (LSI), and Shannon Diversity Index (SHDI) were the core driving factors influencing soil erosion in the southwestern alpine canyon region. Notably, the explanatory power of single and double factor interactions on soil erosion showed a weakening trend year by year. A comprehensive analysis indicated that the explanatory power of landscape pattern changes on soil erosion was gradually weakening, and its impact on soil erosion has gradually shifted from "dominant" to "basic regulation". This shift marked the driving factors of soil erosion in the southwestern alpine canyon region transitioning from an early "landscape pattern-dominated type" to an "external forcing factor-driven type". In the future, regional soil and water conservation management needs to shift from a single "landscape optimization" to a coordinated governance model of "landscape optimization +climate change adaptation + human activity regulation".