Dust could be generated due to the interaction between hot plasma and wall materials in the ITER vacuum vessel, in which hydrogen could be generated when induced by water or steam reacting with dust in some hypothesis accident scenarios, such as loss of coolant accident, wet bypass and loss of vacuum accident. Under such conditions air ingress may led to hydrogen explosion which could damage the integrity of ITER device and would cause the radioactivity releasing to the environment. Computational fluid dynamics method is proposed to study the distributions of the hydrogen, steam and air in the ITER devices and evaluate hydrogen risk control with inert gas injection and hydrogen removal with passive autocatalytic recombination. To verify the computational models to study hydrogen risk induced by wet bypass accident, STARDUST experiment is modeled and simulated, in which the calculated results compared with the experimental results show that RNG k-epsilon turbulence model can be used in the hydrogen distribution analysis. The calculated results of the hydrogen distribution show that there is hydrogen combustion or explosion risk under the accident conditions. Then the hydrogen mitigation measures is applied to the system, and the analytical result shows that inert gas injection at the early stage of the accident with a large rate could mitigate the hydrogen risk effectively, and that hydrogen recombiners play an important role to mitigate the hydrogen risk in suppression tank, which is helpful for the safety design.