Taking typical accumulative Hefeng landslide in the Three Gorges Reservoir as an example, four major controlling factors are constituted scientifically to establish the geological model of the landslide.  A numerical-mechanical model was established considering emphatically the external reservoir water effect. Then the deformation trend of landslide was forecast for next hydrological year by the extension of the step. The prediction method not only considers the based engineering geological model of landslide, but also considers the effects of groundwater, and it overcomes the shortage of pure mathematical prediction methods.