Abstract: With gradual development of offshore substations towards lightweight, the design of topside structure of the substation is becoming more refined and compact, which puts higher requirements on the safety analysis of the structure.To ensure the safe and stable operation of the lightweight offshore substation in complex marine environments, a safety design assessment of the offshore substation is carried out according to the Fire and Explosion Analysis (Fire and Explosion Analysis, FEA) method. An offshore substation located in the Bohai Sea is taken as the target object. Firstly, the hazard sources to the target offshore substation are identified. Then, simulation calculations are carried out for the working conditions with higher hazard levels through three-dimensional CFD software. Finally, the damage to the offshore substation caused by fire and explosion is evaluated. The results indicate that there are some hazard sources to the target offshore substation, among which the hazard sources with higher risk level are the main transformer system and the diesel engine system. It is revealed by calculations that under the case of major leakage the maximum heat flux density (160 kW/m²) and the explosion over pressure value (28 kPa) of the diesel generator system can occur, of which the maximum heat flux density is lower than the fire damage threshold and the maximum explosion over pressure value has a lower probability of occurrence. Therefore, under the current passive design of fire and explosion protection, the fire and explosion will not cause severe damage to the main structure. This study can provide references for the structural design and security maintenance of lightweight offshore substations