Abstract: To determine the thermal insulation property of the heat-proof materials cladding the instrument and cables, a thermal vacuum test scheme is designed and implemented, with a radiant heat source simulated by a quartz lamp heater, and the atmospheric environment simulated by a vacuum tank. The thermal insulation properties of seven assorted groups of protective structures are characterized by the temperature measured at two points on the inner and outer surfaces of the protection material under a heat flux of 20 kW/m² during 800 seconds. The candidates are put in the order of the superiority after evaluation of the results. Suggestions are then made for the selection of heat-proof structures in the radiant thermal environment. In the context of this test, the combination of the glass fiber strip (two layers)+the silicone rubber cloth (two layers)+the aluminum film (two layers) gives the most desirable result of 192 ℃ at the inner surface, which is adequate within the upper limit of the working temperature of the cable core. The test data may serve as a reference for the heat-proof design of rockets in the atmospheric flight stage.