To study whether there is liquid oxygen in the hydrogen–oxygen torch igniter and further study the influence law of liquid oxygen droplet diameter, simulations were carried out based on k-ε, EDC, and DPM models. The simulation results between the pressure boundary condition and the mass boundary condition of the oxygen inlet of the igniter are much different from the experimental values, which proves that liquid phase oxygen exists in the oxygen inlet. The impact of varying oxygen droplet diameters is analyzed by simulations, including 1 μm, 10 μm, 50 μm, 100 μm, 500 μm, 700 μm, 1000 μm, and 1500 μm. The simulation results show that the igniter outlet temperature rises as the oxygen droplet diameter increases when it is not fully evaporated. The oxygen-fuel ratio mainly determines the outlet temperature of the igniter and is little affected by the inlet oxygen phase state. The igniter outlet temperatures in all the conditions exceed 1000 K, ensuring successful ignition of the main engine.