Abstract: To address the limited energy conversion efficiency of organic Rankine cycles (ORC) in liquefied natural gas (LNG) cold energy power generation and the high energy penalty of air separation units (ASU) in semi-closed supercritical CO₂ (sCO₂) cycles, this paper proposes a novel semi-closed sCO₂ power system coupled with LNG cold energy and ORC, replacing ASU oxygen supply with green oxygen byproduct from water electrolysis. Comprehensive thermodynamic and economic analyses are conducted. Under baseline conditions, the system achieves an overall energy efficiency of 62.06%, a power exergy efficiency of 49.12%, and a levelized cost of electricity (LCOE) of 118.48 \/MWh. Sensitivity analysis demonstrates that increasing turbine inlet temperature improves thermodynamic performance while yielding a non-linear LCOE trend that first decreases and then increases; higher turbine inlet pressure enhances thermodynamic performance but elevates power generation cost; whereas higher turbine outlet pressure simultaneously degrades both thermodynamic and economic performance. Following NSGA-II multi-objective optimization, the power exergy efficiency increases to 50.13% while the LCOE drops to 117.7 \/MWh. The proposed system enables cascaded LNG cold energy utilization, green byproduct oxygen reuse, and centralized separation of combustion-generated CO₂, offering valuable theoretical guidance for the integrated design and parameter matching of cold-energy power systems at LNG receiving terminals.