Abstract: Vegetation can effectively suppress shallow landslides. But landslide,debris flow and other disasters also occur in areas with good vegetation under special circumstances such as rainstorm. Due to the numerous factors affecting slope stability by different vegetations,it is difficult to assess slope stability and disaster risk. So there is no preferable evaluation or assessment method. In view of this situation,the Dadu River Basin is chosen as the research area. Through the regional terrain,slope,vegetation data extraction and slope division,the numerical calculation method of finite difference is adopted to calculate the stability of more than 40,000 slopes divided in the region. Then the factors of safety of slopes under different vegetation covers are obtained. Based on vegetation type,slope,it is found that different types of vegetation cover conditions of unstable slope gradient distribution have a normal slope stability of law. Based on the results of all potential unstable slope's vegetation type and grade of statistical analysis and distribution characteristic,we set up three different vegetation types of unstable slope development function relation between probability and slope. The calculation results show that as the slope increases,the number of stable slopes for different vegetation types decreases to different degrees. In general,arbor forests cover slopes have poor stability,followed by shrubs,and the meadows were better. In addition,the slope range with the highest probability of unstable slope development is different: 26.0°~37.0°for arbor forest,28.0~39.0°for shrub,and 31.0~39.0°for meadow. This study can provide a basis for the prevention and planning of landslide,debris flow and other geological disasters in the basin,and also provide more reliable data and ideas for the quantification of indexes and determination of weights in disaster risk assessment of good vegetation areas.