Abstract: To investigate the influence of electricity market mechanisms and ancillary service subsidies on the operational optimization of electricity-hydrogen systems, this study develops an hourly power-net profit optimization model. A 100 MW alkaline electrolyzer system, composed of twenty 5 MW units, is selected as the case study. The model integrates time-of-use electricity pricing, ancillary service subsidies, and parameter sensitivity analysis within a coordinated electricity-hydrogen coupling framework. Three scenarios—valley, mid-level, and peak pricing—are designed to quantify the electricity market effects on hydrogen production strategies. The nonlinear adjustment effects of ancillary service subsidies on system profitability are analyzed. The results show that time-of-use pricing significantly directs the optimal dispatch: under valley pricing, breakeven is achieved at 14% rated hydrogen production power and net revenue peaks at full power load; under mid-level pricing, the system operates all at a loss with an optimal load power of 63%; under peak pricing, the system minimizes loss by operating at 8% power. Ancillary service subsidies introduce nonlinear optimistic impacts on dispatch decisions: at 0.1  CNY/kWh, the system breaks even under both mid and peak pricing scenarios via load adjustment; at 0.2−0.4  CNY/kWh, the optimal strategy shifts from hydrogen production-oriented to ancillary service-oriented, reducing the optimal load to 21% in valley scenarios. Sensitivity analysis indicates that green hydrogen prices have a greater influence on optimization outcomes than fixed costs. While fixed costs linearly affect net profits, hydrogen prices introduce nonlinear effects, partially mitigated by subsidy mechanisms. This study reveals the coupling mechanisms between electricity market signals and service subsidies in electricity-hydrogen optimization, offering a technical basis for hydrogen system dispatch strategies and electricity market design.