Abstract: The computational model of radionuclide activities in reactor compartment was set up for the nuclear accident of nuclear ships.The effect on the reducing of radioactive concentration by emergency ventilator was calculated quantitatively.It showed that the emergency Ventilation had a significant effect on the reducing of the radiological consequence,the reduction effect depends on the ratio of ventilation flux to the net volume of the reactor compartment,and the greater the ratio,the faster the reduction.Within half an hour after the emergency exhaust operated,the activity in the reactor compartment can be reduced by 90%.