Abstract: A method for a whole-process numerical simulation and hazard forecast of a mountain disaster is provided. The method includes: S1, a high space-time rainfall forecast of a mountain area; S2, a hydrodynamic process and numerical simulation: establishing a hydrodynamic process model and solving the hydrodynamic process model; S3, a motion model and numerical simulation of a mountain torrent and debris flow disaster; and S4, a risk analysis and hazard forecast of a small watershed disaster. The present invention predicts disaster hazard and dynamically and quantitatively evaluates risk loss according to a whole-process scenario simulation of the disaster driven by a climate forecast result, improves current disaster level forecasts to hazard forecasts, and serves for accurate disaster preventions and accurate rescues.