The effects of zero equation model and k-ε model on hydrogen distribution have been analyzed by computational fluid dynamics program CFX, and the hydrogen distribution characteristics in the reactor space of marine reactor under typical water loss induced severe accident could be numerically simulated. The results show that it is more reasonable to use the k-ε model to simulate the hydrogen distribution in the reactor space during the concentrated release stage of hydrogen. During the period of severe accidents, the pressure changes at each point in the reactor space could be regarded as basically the same, and the temperature in the space will not continue to rise. Hydrogen forms a relatively obvious concentration gradient in the reactor space. At the top area of the reactor space and the area near the break the hydrogen concentration is abviously rising. After the hydrogen injection, the average vapor concentration in the reactor space is not high enough to maintain the inert environment, and there is a possibility of hydrogen combustion in the reactor cabin space. This study provide a basis for the research of hydrogen risk of marine reactor.