Abstract: The “23•7” extreme rainstorm not only caused widespread flooding in North China, but also triggered numerous geological hazards in the mountainous regions of Beijing. This study focuses on the debris flow event in Fanjianggou, Wangping Town, Mentougou District, induced by the “23•7” rainstorm. Based on a comprehensive analysis of the geological background of the area, the developmental characteristics, triggering mechanisms, and evolutionary process of the debris flow were systematically investigated. Taking into account the local topographic and geomorphological features of Fanjianggou, an integrated mitigation strategy consisting of "source stabilization + flow diversion + blocking + drainage" was proposed, with "flow diversion" as the core control concept. Additionally, a novel "water-sediment separation" structure was also introduced into the blocking measures, effectively protecting downstream villages along the gully. The proposed "flow diversion" strategy and the innovative " water-sediment separation" structure provide valuable references for similar debris flow mitigation efforts, and have significant implications for disaster prevention and control in mountainous regions of Beijing.