Abstract: Gold mining operations were very active in the Dahu valley, Linbao City, Henan Province, and plenty of mine slagheaps became the main source of the debris flows. According to the characteristics of the slag-type debris flow and on-the-spot investigation of the slagheaps in the valleys in 2007, the authors assessed the risk degrees of debris flows in the main course and tributaries of the Dahu valley by using six factors, i.e. slagheap size, clogging degree of the watercourse, slagheap stability, longitudinal slope ratio of the valley, river curvature and catchment area of the valley, whose weights were established using the analytic hierarchy process. The results indicate that 10 of the 13 valleys are high-risk areas, of which the Heiyuzi gully and the main watercourse of the East valley and the East Caotong valley and West Caotong valley of the West valley are very high-risk areas of debris flows. The hidden trouble of slag-type debris flow in the Dahu valley was very serious. The assessments provide a scientific basis for the early warning, prevention and control of debris flows in the Dahu valley.