The landslide—blocking river—dammed lake disaster chain is a typical disaster in mountain and gorge areas. The interaction between landslides and rivers, as the linking process in this disaster chain, often determines the scale of continuation of subsequent disasters in time and space. It is critical to reproduce the complex fluid-solid coupling process in the assessment of the landslide-blocking river disasters. By using the Drucker–Prager model to simulate the sliding of the landslide body, along with an artificial equation of state to model the flow of water, the two-phase double-point material point method (TPDP–MPM) program was developed. The simulation of the landslide-water body interaction process on an experimental scale was conducted and verified the reliability of TPDP–MPM in multiphase coupling problems. On this basis, a landslide—dammed lake disaster chain, namely the Pingdu River being blocked by the Erhuang Village landslide, Shiyan City, Hubei in 2011, was reproduced by the TPDP–MPM program. According to the TPDP–MPM simulation results, this disaster could be divided into four stages: unstable initiation, high-speed sliding, river braking, and accumulation. Based on the velocity field of the landslide mass and the evolution of the kinetic energy, the sliding pattern of the Erhuang Village landslide and the mechanism of river braking were revealed. The research results provided a theory and method for the whole process analysis and risk assessment of the landslide—dammed lake disaster chain