A typical area should be chosen as the sample area in a region that will be zoned. The information of debris flows must be gathered completely. The risk factor zones are zoned according to the complete information of debris flows. The relative altitude, stratum, lithologic characters, fault, earthquake, annual variability of precipitation, interannual variability of precipitation and the daily range of temperature are selected as the main factors influencing the activities of debris flows, and the statuses of these factors are divided. The information quantities of all statuses of the main factors to different risk factor zones are calculated as the base on the concept of information quantity in the information theory. Different risk factor zones constitute a remark set. The general information quantities of every factors to different zones constitute a fuzzy evaluation set. Then the risk factor zones are determined with the principle of maximum membership grade according to the remark set and fuzzy evaluation set.