Abstract: The measurement of the solar absorptance as and the hemispherical emittance AH were performed by the caloric method for opticalsolar reflector(OSR)that will be applied on the comnlunicationbroadcasting satellites.In order to calculate the temperature distribution of thesatellites correctly,the thermal radiation properties of the compositeOSR samples were measured.At the same time the solar absorptance of aOSR sheet was measured by both the caloric method and the spectralmethod for comparison.The measured results and the difference betweenthem were analysed.The analyses indicate that the normal solar absorptance αs.of a OSR sheet should not be taken as a design parameter,otherwise a larger error will happen in temperature calculation.