Abstract: The variation trend analysis on debris flow scale of Zhamunong Gully is the basis for further analysis on the frequency of potential giant debris flow. Based on borehole data, field survey data and relevant literature, we determine the variation process of the debris flow scale under ten thousand years scale by using Optically Stimulated Luminescence method and debris flow parameter calculation method. According to the variation process and the condition of endogenic and exogenic geological processes at present, we research the future development trend of the debris flow in Zhamunong Gully. The results show that: (1) the debris flow scale decreases under ten thousand years scale in fluctuation, the giant debris flow scale also decreases, and the confluence-type debris flow scale also gradually reduce during the decades after the occurrence of giant debris flow. (2) There still has endogenic and exogenic geological processes conditions in Zhamunong Gully and the giant debris flow is prone to occur after a period of time(maybe thousand years scale or century scale), but the scale would be less than the giant debris flow in 2000. After the giant debris flow, many other disasters would continue for a while.