In the face of increasingly serious energy and environmental problems, the safety of offshore oil drilling and production platform, as a natural gas development platform, is of great significance. For offshore platforms, the offshore power system serves for oil and gas production, and the interruption or shutdown of oil and gas production caused by electric power is intrinsically unsafe; In addition, due to the weak interconnection between the offshore platform systems, with the characteristics of small unit, large load, wide application of frequency conversion equipment and poor environment, the security analysis of the offshore platform power system must take the power grid and gas network as a whole to analyze and take into account the low-voltage crossing capacity. For the coupling of power grid and gas network of offshore platform, multi-stage compression system and the "power to gas" system are proposed. For these voltage sag sensitive systems, the safe critical voltage and critical cutoff time are used to characterize the low-voltage crossing capability. The operation constraints considering the low-voltage crossing capability are also proposed, and the impact of voltage sag is taken into account in the safety analysis. The simulation results show the correctness of the safety analysis method considering the low voltage crossing capability, and the necessity of the safety analysis considering the gas network and the low crossing capability. INDEX TERMS Offshore platform power system, low voltage crossing capability, safety analysis.