Abstract: A fuel cell ship carries a large amount of hydrogen as fuel,which brings threat to safety of the ship owing to characteristics of hydrogen as easy to leak or explode.A 3D geometric model of fuel cell cabin from a target ship is established to develop a scenario of hydrogen leakage happening in the cabin.On the basis of this model,the leakage rate of hydrogen from pipeline is computed by defining an ideal gas model and leakage parameters.Afterwards,transient leakage and diffusion processes of hydrogen in the fuel cell cabin are simulated by fluid computation software Fluent and gas diffusion equations.Finally,distribution law of hydrogen concentration and dispersion trends are compared under different ventilation conditions of open/close doors and air vents.The simulation results show that the hydrogen concentration is higher in the top four corners of the cabin,which are the optimal places for hydrogen detection.Moreover,keep doors open can reduce the final concentration of hydrogen by about 20% under the condition of natural ventilation.When ventilation rate of single vent is 6 m3/s,the dispersion mole fraction to other cabins can be kept under a safety level of 4%,while concentration of hydrogen in the cabin can be kept at a low level.Continually increase the ventilation rate has less effectiveness to lower concentration of hydrogen.