Abstract: The large-scale hydrogen station accident was simulated under ventilation conditions. Based on one-dimensional local inviscid characteristic analysis, a three-dimensional Navier-Stokes non-reflection characteristic boundary condition for reacting flow using ghost cells was developed. By introducing transverse term and chemical reaction source term, non-physical reflection generated by flame and subsonic flow interacting with boundary was effectively eliminated, which realized the non-reflection application of ventilation conditions at the computational boundary and improved the computation efficiency of open space numerical simulation. Numerical simulation of accidental hydrogen leakage and diffusion of long tube trailers and filling machines of 51 m×51 m×10 m hydrogen station was carried out, and the distribution result of flammable gas cloud under various ventilation conditions was reported. The impact of complex environments on the development of flammable gas clouds was quantitatively analyzed. The most dangerous hydrogen leakage and diffusion result was selected to carry out numerical simulation of highly inhomogeneous gas cloud explosions, the overpressure and impulse received at different places of the equipment was analyzed, and the risk assessment of typical accidents in hydrogen refueling stations was completed.