The invention relates to a switch of a thermal control system for a temperature sensing device, in particular to a thermal switch of a thermal control system for a spatial camera. The thermal switch comprises a left heat conducting block, a right heat conducting block, a movable heat conducting block which can transversally move between the left heat conducting block and the right heat conducting block, a telescopic rod made of materials with the thermal expansion coefficient larger than that of the left heat conducting block, the right heat conducting block and the movable heat conducting block, and a spring. Both the left heat conducting block and the right heat conducting block are provided with blind holes with openings towards the movable heat conducting block; the telescopic rod and the left heat conducting block are arranged in the blind hole of the left heat conducting block in a sliding fit manner; and the spring is arranged in the blind hole of the right heat conducting block. The movable heat conducting block is achieved to be respectively in crossed contact with the left heat conducting block and the right heat conducting block to change a thermal conducting channel through the thermal expansion and the cold shrinkage of the telescopic rod. The thermal switch has the advantages of simple structure, high reliability and long service life, and can achieve the automatic temperature control function of the temperature sensing device.