In order to solve the problems that may occur in high and steep tailings slope with cracks during rainstorm and continuous heavy rainfall, a tailings slope in Ganzhou City, Jiangxi Province is used as the prototype of the calculation model in this paper, and a two-dimensional slope model with a height of 8.5 meters and a slope angle of 60° is established.Based on MatDEM, numerical simulation of water content, displacement change, coordination number and unit velocity are carried out, and the evolution law of displacement field, water field and fracture are obtained.The simulation results show that the numerical simulation model of rainfall-induced landslide can be summarized as “rain Infiltration slopes and fissures-failure at the bottom of the slope-disconnection of the fracture elements-complete failure of the slope”.The change of unit water content is mainly affected by the influence of cracks on water migration in addition to many factors such as the location of the unit in the slope and the water content gradient.During the whole process of the high-steep slope sliding, the total amount of moving slope units has been stable within an interval without major changes.The research on the evolution mechanism of fracture rock mass instability based on MatDEM, could help predict and prevent landslide disasters very well, and has a certain guiding effect on actual production.