Abstract: The mountainous areas in southwestern Sichuan Province, China, are prone to dry winters and springs, which create favorable conditions for frequent forest fires. During rainfall events, slopes in burned areas are highly susceptible to intensified soil erosion, thus significantly increasing the risk of post-fire debris flows. Therefore, identifying the spatiotemporal evolution characteristics of slope erosion in burned areas can effectively underpin the comprehensive prevention and control of post-fire debris flow disasters. This study focused on the burned area affected by the “5•7” forest fire in Houshan, Zhongba Village, Xide County, Liangshan Prefecture, Sichuan Province in 2020. The spatiotemporal evolution characteristics of slope erosion and the dynamic reserves of slope material sources for post-fire debris flows in the burned area from 2019 to 2023 were analyzed. The results indicated that the average slope soil erosion modulus in the study area was 1175 t/(km²·a) in 2019, and the dynamic reserves of slope material sources was 950 m³. In 2020, the average slope soil erosion modulus increased to 17771 t/(km²·a), and the dynamic reserves of slope material sources rose to 13792 m³. By 2023, the average slope soil erosion modulus decreased to 3421 t/(km²·a), and the dynamic reserves of slope material sources decreased to 2457 m³. Forest fires caused a sharp increase in soil erosion modulus and dynamic reserves of slope material sources in the burned areas of the study region, and the increase is positively correlated with fire intensity. Subsequently, as vegetation gradually recovered, both the soil erosion modulus and the dynamic reserve of slope material sources in the burned areas decreased, but still higher than the pre-fire levels, indicating that the slope erosion in the burned area has been impacted for more than 3 years.