A temperature adjustment system for a passenger support device comprises an air circulation loop. The air circulation loop comprises: an air distribution layer; a main power device for causing circulation of air in the air circulation loop; and a temperature adjustment device for adjusting the temperature of the air in the air circulation loop. An air flow flows out of the main power device after its temperature has been adjusted by the temperature adjustment device. The air flow at least comprises a first portion flowing into the air distribution layer and a second portion returning to the main power device after passing through the interior of the air circulation loop. After the temperature of the air flow returning to the main power device has been adjusted again by the temperature adjustment device, said air flow continues to flow in the air circulation loop. Also provided are a seat cushion and backrest comprising the above temperature adjustment system and a passenger support device comprising the seat cushion and/or the backrest. The passenger support device can be a chair or a bed. The passenger support device adopts a closed or semi-closed air-circulation loop, thereby quickly providing heating or cooling to a space around the passenger support device, and achieving a favorable heating or cooling effect, namely a higher temperature in a heating operation or a lower temperature in a cooling operation.