A nuclear reactor serious accident fragment bed melting process simulation method based on a particle method comprises the following steps of 1, conducting particle modeling, setting particle initialarrangement and parameters, using particle clusters for representing solid fragments, and numbering the particles and the fragments respectively; 2, dividing background grids, and retrieving neighborparticle groups; 3, explicitly calculating a viscosity item, a surface tension item and a gravity item in the momentum equation, and estimating particle speed and displacement; 4, calculating particlepressure by adopting a Poisson equation, and correcting particle speed and displacement according to a pressure gradient model; 5, calculating a particle enthalpy value, a temperature and a phase state; 6, calculating the translation speed and the rotation speed of the fragments, and correcting the speed and the displacement of the solid-phase particles in the fragments; 7, outputting a calculation result. According to the method, small-scale particles are used for representing large-size solid fragments and numbering the large-size solid fragments, so that the identification problem of the fragments to which the particles belong is solved. In addition, a radiation heat exchange model between the solid fragments is established according to a mode of judging whether two particles are shielded by other particles or not.