In order to solve the problem that the efficiency of traditional gas displacement based on the mode of charging and holding in sealed cabin was not high, the gas displacement model of sealed cabin was established by using the continuous gas replacement mode, charging and exhausting at the same time. The numerical simulation was carried out by using the RNG κ-ε epsilon model. The results show that with the increase of charging time, the gas displacement rate gradually increases, but the increasing rate decreases, the greater the charging rate, the higher the gas displacement rate; when the charging pressure is higher than the pressure in the cabin, the charging gas pressure has little effect on the gas displacement rate; charging and exhausting at the same time can increase the displacement rate in the initial stage of gas displacement, but with the increase of time, the method can not increase the efficiency of gas displacement.