It is necessary to obtain the evolution process of plate fuel melting accident, to prevent the continuous melting and spread of the core fuel after the accident of flow channel blockage. Therefore, a two-dimensional geometric model of 1.5 components of a typical dispersed plate fuel experimental reactor JRR-3 M was established, and the volume of fluid (VOF) method coupled with enthalpy-porosity method was employed to simulate the process of fuel melting and melt migration spread after the flow channels of JRR-3 M hot assembly completely blocked. The simulation results show that the melt continuously contacts with the adjacent fuel plates during its downward migration, resulting in the burning of the adjacent fuel plates. The complete blockage accident in the JRR-3 M hot assembly ultimately caused the melting of three fuel plates within the average assembly. However, the fuel melting accident did not further propagate, and the reactor remained in a controllable state.