In order to improve the thermal conductivity of materials and decrease the temperature gradient of a space optical remote sensor, the carbon-carbon composites were pasted on the metal surface. The characteristics of carbon-carbon composites were introduced and the heat transfer models of one bare steel plate and two pasted plates with carbon-carbon composites in the thicknesses of 0.5 mm and 2 mm respectively were established. The three heat transfer states of the steel plates were calculated and experimented, and their equivalent thermal conductivities were obtained. The models were simulated by using the finite element model IDEAS-TMG and the heat transfer properties of three kinds of plates mentioned above were compared. Results is shown that the carbon-carbon composites could improve the temperature uniformity of the plates. Finally, the carbon-carbon composites were applied to a TC4 star-tracker bracket of a star sensor, and the temperature difference between the assembly area and the radiator was tested. The tested results indicate that it is 28 ℃ and 5 ℃, respectively, for the bare bracket and the one with 0.5 mm-thick carbon-carbon composites on the inner and outer sides. The tested result illuminates that the thermal conductivity of the bracket of the star-tracker is improved and its temperature gradient is reduced effectively. This method could give some guidances and references for the thermal design of other space optical instruments with great temperature gradients.