Abstract: According to the characters of nuclear reactor used in boat, the simulation software for square fuel assembly nuclear reactor used in power plant was transplanted and reworked, and a simulation software for ship hexagon fuel assembly uncleaned nuclear reactor was developed. It was used to simulate the xenon poison in ship nuclear reactor with the burnup of 30 MW•d, and the simulated results were compared with that from point model. It is found that the simulated results of point model are smaller. Besides the deviation between simulated and actual equilibrium xenon reactivities is -0.8%, the deviation is -4.3% for maximum xenon reactivities, and the deviation is -0.5% for iodine well reactivities. The simulated results from present software accurately indicate the characteristics of xenon poison for a ship nuclear reactor.