Abstract: The pressure difference of inside and outside the orifice of a sealed cabin in the re-entry flight is studied, and the variable gas charging process of the orifice is analyzed. A discretized analytical method is used for the calculation of a sealed cabin with a volume of 14 m³ and an orifice with an area of 10 cm². The pressure difference of the sealed cabin, the mass flow rate, and the gas velocity in the orifice against the time or height are obtained. The results show that at the height of 5 km, the mass flow rate reaches its highest value of 0.134 kg/s; the pressure difference approaches the maximum; the gas velocity ranges between 148.4~181.5 m/s(in the subsonic zone); and the gas velocity in the orifice is related only with the inlet and outlet pressure of the orifice and the inlet gas density, while regardless of the area of the orifice. The above results may provide a reference for the design of capsule structures and parachute-module systems.