【Objective】 Straw return is vital for improving soil structure, controlling erosion, and mitigating degradation. Nevertheless, the low straw decomposition efficiency under natural conditions greatly limits its widespread application. As a critical measure to promote straw decomposition, investigating the impacts of straw returning combined with decomposition agents on soil erosion resistance of medium-low yield sloping farmland, as well as the underlying mechanisms, holds significant importance for applying soil and water loss control measures that integrate the resource utilization of agricultural waste.【Methods】 A field in-situ monitoring experiment was conducted under the condition of full straw return. With no decomposition agent application as the control, four straw decomposing agents were co-applied with straw at rate of 1, 2, 3, and 4 kg·hm-2 and designed based on the viable bacterial count of the decomposer. The differences in soil erosion resistance and their dominant influencing factors under varying decomposer application rates were clarified.【Results】 The application of straw decomposition agent significantly promoted straw decomposition efficiency and improved soil structure. The straw decomposition amount and efficiency increased significantly with the increase in the application rate of the decomposition agent. Also, application of decompositing agent significantly reduced soil silt and clay contents, while significantly increasing soil sand content, saturated water content, field capacity, and organic matter content. Moreover, the soil erosion resistance was significantly improved with the application of straw decomposition agent. Compared to the control, the comprehensive soil resistance index (CSRI) increased by 43.24% ~ 360.77%. In addition, the results of PLS-SEM showed that the increase of CSRI was mainly governed by the direct binding and consolidation of residual straw (path coefficient 0.43) and the indirect effect of straw decomposition on the increase in soil organic matter content (path coefficient 0.40).【Conclusion】 Straw return combined with straw decomposition agents significantly increased soil erosion resistance of medium-low yield purple sloping farmland. Moreover, the direct effects of residual straw in enhancing soil erosion resistance slightly outweigh its indirect effects in increasing soil organic matter content via decomposition. However, a significant increase in CSRI was only detected when the application rate exceeded 3 kg·hm-2. This indicates that effective enhancement of erosion resistance requires a threshold application rate exceeding 3 kg·hm-2 for decompositing agents. These findings provide scientific guidance for the sustainable utilization of medium- low-yield purple soil sloping farmland and the green and high-quality development of the Yangtze River Economic Belt.