Abstract: This paper presents an automatic hierarchical approach to detecting avalanches, landslides and debris flows by the combination of multi-spectral RS images and DEM derivatives, which identifies these geohazards by six boolean operations based not only on their reflectance but also on geometric shapes and their geomorphic context. Corresponding experiments with 10 m resolution RS imagery and 1:50,000 scale DEM in the Biluo Mountain gorge were performed to check the results of automatic recognition of the avalanche, landslide and debris flows. The results demonstrate that: 1) this approach can effectively raise the accuracy of recognition of avalanches, landslide and debris flows with the influences of their geometrical features considered; 2) it is characterized by definite relationship between the data and the recognized objects, simple logistic and easy determination of the threshold; 3) the data sources (i.e. medium-scale DEM and RS imagery with infrared and near-infrared spectra) can be widely obtained；and 4) the main problems of this method is to divide conglutinating pixels.