Abstract: The thermal comfort of the airtight cabin of the Tiangong-2 space lab is assessed using the PMV model based on the flight data, as compared with that of the Shenzhou-11 manned spaceship and the Tiangong-1 target vehicle. The causes of the difference are discussed. The influence of the air temperature, the relative humidity and the temperature of the cabin wall on the thermal comfort are discussed in detail, which indicates that the air temperature is the most important factor. The result may serve as a reference for the thermal design of subsequent manned spaceships.