A thermal spike model has been established and the high energy damage of UO2 was simulated by a molecular dynamics method. Different input temperatures and different input radii were set in single thermal spike simulation. The atoms in the central zone are activated by the thermal energy and passes to the outer layer with pressure wave style fast. The recovery happens simultaneously with a vast number of departure atoms. The final configurations are three types including amorphous, semi-amorphous and crystal. The simulation results can reproduce the physical process of thermal spike irradiation well. The affected zone which is too tiny to be viewed by experimental instruments can be observed directly