Abstract: A numerical model based on Eulerian-Eulerian multi-phase flow model is established to back-calculate the behavior of the submarine landslide identified in the deep water off the northwest coast of Sumatra. Compared with the BING results and analytical results, the numerical model with the consideration of soil strength reduction can provide a valuable mass movement process for the submarine landside, with final deposition patterns and runout distance similar to the identified parameters. The result shows that:the landslide takes place firstly at the part with larger slope angle, and then the left part with lower slope is pushed forward; the landslide is accelerated gradually along the slope, until reaching the slope toe with a peak front velocity of 43 m/s, then it is decreased gradually and stopped on the abyssal plain. Soil strength reduction, caused by disturbance and invasion of ambient water, is the basic reason for the longer runout distance of the submarine landslide. Hydroplaning was proved to occur during the movement, which could reduce the seabed friction and promote the moving distance obviously.