Abstract: Space nuclear reactors have gained increasing importance in deep space exploration missions, with launch abort scenarios leading to ground surface impact representing a core consideration in reactor safety design. However, space nuclear reactors cannot incorporate the same degree of redundancy and diversity as terrestrial nuclear facilities. Throughout their mission lifecycle, space nuclear reactors may experience atmospheric re-entry and subsequent ground surface impact at any stage. During hypervelocity impact events, the extreme kinetic energy induces severe structural deformation in the reactor pressure vessel. This deformation process may compromise safety-critical components such as control drums, fuel pins and restraint mechanisms, potentially affecting the reactor’s neutronics characteristics. Consequently, conducting structural integrity assessments under various impact conditions provides essential data for criticality safety evaluations and serves as the basis for design optimization. This study employed the TOPAZ-Ⅱ space nuclear reactor as the research subject. Finite element simulations of terrestrial and aquatic impact behavior under various accident scenarios were conducted using ANSYS/DYNA and ABAQUS software. Based on finite element principles, Eulerian and Lagrangian methods were utilized to simulate reactor impacts. The structural response, component damage, and the influence of different failure criteria and motion parameters were investigated. The most severe damage to the space nuclear reactor occurs during ground surface impact at 0°. At this orientation, fastener failure initiates at low velocities, causing reflector assembly and control drum detachment. Additionally, safety control rods exhibit ejection propensity within the 16-68 m/s impact velocity range, whereas no ejection is observed at impact angles exceeding 21°. In contrast, water body impacts cause relatively minor damage to the space nuclear reactor, with no ejection risk has been observed. The reactor structure remains largely intact at impact velocities below 100 m/s, whereas fuel element dispersion occurs at velocities exceeding 200 m/s. At impact angles of 45° and 90° with velocities of 100 m/s and 150 m/s, the reactor faces a critical risk scenario. Under these conditions, the reflector layer and control drums detach, safety rods undergo partial destruction, and the reactor core becomes submerged in water body. Complete structural failure of the reactor vessel and fuel element dispersion occur at impact velocities above 200 m/s. The impact of a space nuclear reactor on both ground surface and water body presents critical safety risks. In the case of ground surface impact, the primary hazard arises from the potential ejection of safety rods and the detachment of the reflector layer and control drums. These results deliver fundamental inputs for criticality safety assessments and establish reference frameworks for test parameter definition and experimental configuration design in space nuclear reactor terrestrial impact experiments.