Abstract: Hillslope debris flows are the major geological hazards in East China. It is very important to predict these dangerous phenomena. Three groups of conditions related to topography, geology and hydrology have influence on the triggering of these hillslope debris flows. We isolated and analyzed the influence of the topography on the triggering of hillslope debris flows in catchments with almost identical hydrological and geological conditions and propose a new so called T-condition as a topographical indicator which is a combination of slope angle, upslope contributing area and cross-section and free-face of a (potential) hillslope debris flow. The T-condition can be used to define threshold values for possible hillslope debris flow development. Higher T-condition values are related to higher probabilities of debris flow events. An R-condition is used as a rainfall indicator, which is a combination of the antecedent one hour rainfall, the antecedent cumulative rainfall and the annual rainfall. Higher R-condition values are generally related to higher probabilities of hillslope debris flow events. The prediction condition P, which is the combination of T and R, gives a final indication of debris flow probability and it can be used to define threshold values for the hillslope debris flows.