The formation conditions of debris flow were analyzed and the seven key indexes of hill slope, elevation, hill surface roughness, rock stratum, distance to faults, seismic intensity of earthquake and land use type were chosen for evaluating the susceptibility of debris flow. A model of debris flow susceptibility was established by introducing logistic regression, and the evaluation and mapping of debris flow susceptibility were completed for the highways. Subsequently, this proposed method was applied in a case study carried out on the Sichuan-Tibet section of national highway G318. Analysis of debris flow susceptibility for the whole highway showed that 78.61% of the total study area was situated in debris flow-prone areas, including the canyon areas of Dadu, Lanchang, Jinsha, Nu and Palongzangbu Rivers. It is suggested that sufficient attentions should be paid in debris flow forecast and prevention in road reconstruction and line selection for new highway.