Off-grid wind–photovoltaic systems can provide low-carbon power for liquid hydrogen production, but renewable generation fluctuations complicate the coordination of fixed liquid hydrogen output and external electric load supply. This study develops a 24 h mixed-integer linear programming model for an off-grid wind–photovoltaic liquid hydrogen production system with fixed daily output. The system includes wind turbines, photovoltaic arrays, an electrolyzer, a high-pressure gaseous hydrogen unit, a hydrogen fuel cell, a Claude-cycle liquefaction unit, and a liquid hydrogen tank. The model guarantees a daily liquid hydrogen output of 5000 kg through a terminal inventory constraint and minimizes unmet external electric load, renewable curtailment, and hydrogen purchase. Case studies with different renewable generation profiles compare output guarantee, load supply, renewable utilization, hydrogen purchase, and storage behavior. The results show that the terminal liquid hydrogen inventory reaches 5000 kg in all feasible cases. For the typical wind–photovoltaic case, the optimized dispatch achieves zero renewable curtailment while maintaining external electric-load supply. The electrolyzer converts surplus renewable power into gaseous hydrogen, and the fuel cell supplies backup electricity during low-renewable periods, with a peak hydrogen consumption rate of 425 kg/h. The Claude-cycle liquefaction unit produces the required net liquid hydrogen output by coordinating liquefaction with gaseous hydrogen storage and recycle flows. These findings confirm that high-pressure gaseous hydrogen storage can buffer renewable power volatility and support stable off-grid liquid hydrogen production.