Abstract: Collisions and impacts that may occur in launch and reentry phases are the key research contents of radioisotope heat unit (RHU) for space nuclear security. Aiming at the accident conditions of high-speed impact on the ground after accidental reentry of RHU, a dynamic constitutive model of high-speed impact was established based on the design structure and material characteristics of RHU. The effects of velocity and angle on deformation and failure of RHU metal cladding after impact were analyzed by independent variable method. In order to verify the reliability of the numerical model, the high-speed impact tests were carried out. The relative errors of height and diameter deformation of metal cladding (ΔH_max and ΔD_max) are less than 10% compared with the simulation results, which are acceptable errors for engineering simulation calculation. The above results show that the simulation model of high-speed impact has a strong practical value in RHU safety evaluation, guiding RHU design and reducing test cost, etc.