Abstract: As an important barrier for maintaining nuclear safety, the nuclear island pit boss needs to maintain its integrity after a severe accident. Research by scholars at home and abroad on the safety of the nuclear island pit boss under the combined action of earthquakes and Loss of Coolant Accidents (LOCA for short) under severe accident conditions is still relatively limited. Therefore, refined finite element models of different types of nuclear island pit boss components were established based on ABAQUS. By simulating the most unfavorable working conditions of the combined action of earthquakes and LOCA, the stress distribution characteristics, deformation laws and failure modes of various boss components under combined loads were systematically explored. The results show that different types of bosses can still maintain structural integrity under the most unfavorable working conditions, and the arrangement of steel bars can effectively improve their bearing capacity and deformation capacity. The relevant conclusions can provide a reliable theoretical basis and technical support for the optimal design, safety verification and emergency disposal of nuclear island pit bosses, and further enhance the safety resilience of nuclear power plants under extreme combined working conditions.