Abstract: A method for analyzing a sever accident in a nuclear reactor based on an advanced particle method includes steps of: 1) performing geometric modeling, setting initial conditions and boundary conditions; 2) updating material physical properties and key parameters; 3) performing mechanical structure module calculation, updating solid particle stress, strain, internal energy, displacement and velocity; 4) performing thermal hydraulic module calculation, updating fluid particle internal energy, position and velocity; 5) performing chemical reaction module calculation, updating particle matter composition and internal energy; 6) performing neutron physics module calculation, updating particle neutron flux density; and 7) outputting data. The method of the present invention is based on the discrete form of the advanced particle method, which is capable of accurately capturing cross-sectional changes, matter changes, and phase changes.