Abstract: Based on the model of nuclear ship equipment,the tracer diffusion experiments were conducted,with the related systems and facilities simulated in the actual conditions.SF₆ was used as tracer,simulating the radioactive source term.The tracer was released in the reactor cabin,and the concentration of cabins were monitored separately in two different conditions,i.e.,with and without the operation of emergency ventilator.The results were compared and analyzed.The study shows that emergency ventilating could reduce greatly the radioactivity in the ship.The radioactivity in the reactor cabin was reduced over 99% after the ventilator worked 30 minutes,and the radioactivity in other cabins were almost reduced to zero after 5 hours.In comparison,the reduction of radioactivity were not obvious without the operation of the ventilator.