Abstract: Hazard assessment of debris flow is a hot research topic of the disaster science. It is an important task of disaster forecast, prevention and reduction. This paper takes the debris flow gullies atthe dam site in Huoergutu hydropower along Xinjiang Kaidu River as the research area. Based on the studying of the geological environment, it selects eight aspects as evaluation factors. They include debris flow scale, outbreak of the frequency. The weight coefficient of contestant factors is obtained using thegray correlation degree. The risk assessment of debris flow gulliesis evaluated through the qualitative and analogical methods. The results are compared with the results of site-specific debris flowharazd assessment by LIU Xilin. The risk degrees of the Qingshui gully and Xuelian gully using the extension theory are greater than the results of site-specific debris flow harazd assessment, which iscoincided with the filed investigation. Therefore, the grey correlation and extension theory based method for debris flow gullies at the dam site is reasonable and reliable. The method provides reasonable and scientific basis for risk assessment, planning and controlling of debris flows at the dam site.