Mountain flood that causes landslide and other geological disasters can damage the fragile ecological environment in mountain areas. In this paper, threshold and distribution model of accumulated temperature based on snowmelt flood magnitude are designed in mountainous watershed. Meanwhile, input data for this model make use of ample reliable data that include remote sensing and so on. In detail, this model simulates the average watershed temperature by using the meteorologic re-analysis data of the National Center for Atmospheric Research and calculates the average snow depth by using hyperspectral remote sensing data. In addition, the model related data comprise long-term observation experiments of the watershed, including the characteristics of accumulated snow and result of correlation between runoff and infiltration in runoff simulation experiment through distributed hydrological models (i.e., Soil and Water Assessment Tool and Distributed Hydrology Soil Vegetation Model). Finally, the average accumulated temperature of the watershed that causes snowmelt flood can be obtained through the aforementioned method, and the characteristics of the accumulated temperature distribution of the watershed area are determined based on the temperature lapse rate. The characteristics of accumulated temperature distribution can provide decision-making reference for monitoring the ecological environment in mountain areas and preventing and reducing disasters.