Mountain torrents is a kind of flash floods which bring about a great loss of life and damages of properties in mountainous area.in order to support decision making on disaster reduction and prevention,it is necessary for us to evaluate disasters of mountain torrents quickly and correctly. The difficulties in evaluating disasters of mountain torrents lie in the impossibility of hydrologic observation by conventional method because of the grest flowing velocity and washing force and the insufficiency of information got by remote sensing method because of the short duration of mountain torrents.In order to overcome such difficulties,a new method which is an integration of GIS an analytical models is explored in this paper.what we use is an external integration method,i.e.the analytical model is integrated with GIS system as an external procedure.In the process of evaluating disasters of mountain torrents,the role of GIS is to transform vector data into grid data and to query,access,display and analyse grid data;the role of analytical model is to simulate behaviors of water and sand within grid and among grid and to determine the disaster class for each grid.The procedure for evaluation of disasters caused by mountain torrents is as follows:firstly to establish a database including data collection,map digitization and input of tabular data;secondly,to analyse data including DEM analysis,analysis of drainage network and rastering;thirdly,to run the model which includes sekction of simulation parameters,simulation of flood and simulation of sand transprotation within the watershed;fourthly,to evaluate disasters which includes calculation of washing forces,analysis of disaster──bearing capacity and determination of disaster classes.Taking mountain torrents in the Sunhugou watershed on Aug.10,1969 as an example.we tested this methd.The result showes that integration of GIS and analytical mdel is an efficient method for evaluating disasters caused by mountain torrents.GIS promotes establishment of distributed hydrohgic model by management of spatial data; analytical model extends function of GIS by provision of hydrologic information such as water depth,flowing velocity and sedlment concentration.Compositeness of spatial ad temporal information in GIS is an important part in evaluating disasters caused by mountain torrents.Formation of disaster by mountain torrents is a dynamic process in which sufficient information can be got only by simulation of water and sand behaviors.Efficient management and output spatiotemporal information are a subject that need be further studied in GIS.