Abstract: Following the catastrophic “5•12” Wenchuan earthquake, extensive debris was deposited on mountain surfaces in the earthquake zone, and significant vegetation damage occurred, providing abundant material for debris flow outbreaks and substantially increasing their risk. Previous studies primarily focused on vegetation recovery when assessing post-earthquake debris flow risks. However, field surveys revealed that large quantities of dynamic storage materials in the gullies significantly impact risk assessments. Based on field survey data, this study uses Qipan gully in Wenchuan County as a research subject and employs multi-source and multi-scale monitoring tools (Landsat series, Quick-bird, and UAVs) to analyze and statistically assess the source materials on slopes and gullies both pre- and post-earthquake. A dynamic risk assessment model for debris flow is constructed using game theory combined with a cloud model, assessing the risk from 2005 to 2019. Findings indicate that post-earthquake slope material sources were 7.7 times those pre-earthquake, and by 2019, with recovery to pre-earthquake levels by 2019. Statistical estimations based on recorded debris flow eruptions and sediment removal volumes show a reduction of approximately 7.813×10⁶ m³ in dynamic material sources by 2019. Assessing both slope and gully material sources yields more realistic results than considering slope sources alone. These results provide references and guidance for dynamic risk assessments of debris flow, impacting major engineering projects in increasingly seismic regions and effectively ensuring the safety of life and property.