Abstract: Debris flow hazards are an inherent but dangerous and costly element of mountainous environments in the lower Lancang River watershed.Conventional hazard map provide useful inventories of hazardous sites but provide little insight into the potential area of the hazards, this approach tends to rely heavily on subjective interpretation of the landscape.Assessing and predicting mountainous hazards potential using geographic information systems (GIS) are receiving increasing attention over years.Based on the spatial analysis of driving and triggering factors promoting the occurrence and development of debris flows in the Lancang River watershed a database and repository are constructed for assessing the area susceptible for debris flows in the area.A correlation of the occurrence of debris flows with slope gradient, vegetation cover and rainfall are also presented for providing multivariate statistical data available for assessing risk of the debris flows in the area.Using Arc/Info grid module all data in Arc/Info coverage, including contour, vegetation cover and rainfall are transformed into TIN data and DEM and further into raster gradient, vegetation and rainfall with raster of 100m X 100m .With the repository used for assessing the potential of the occurrence of debris flows, The classification of gradient, vegetation and rainfall with five ranks, in agreement with five risk ranks of debris flows :highest, high, moderate, less and none are implemented on Arc/info platform.A digital environmental model (DEM) to assess the debris flow risk in the lower Lancang river watershed.is employed to implement the processes of spatial algebra overlay.Raster gradient, vegetation and rainfall data with a weight of 0.5, 0.3 and 0.2,respectively are imported into same grid environment with to produce a new map, showing the potential zones of the debris flows with different risk ranks of the lower Lancang river watershed.With the overlay of conventional map of the debris flow hazards in history in the area with assessment result, it can be shown that the highest and high risk zones of assessment results are in agreement with the dense zones of debris flows in history and also indicate that the index selected and methods used for assessing the risk of debris flows in the Lancang river watershed are rational and credible for conducting the debris flow disaster control and mitigation in the area.and for helping mitigate the associated risk.