Experimental measurement of radiation temperature by a streaked optical pyrometer and a soft X-ray spectrometer viewing through the laser entrance hole are performed on SG-Ⅲ prototype laser facility. It was found that the two methods compares well. Using the power balance relation，the laser-hohlraum coupling efficiency for 1.0 mm×1.7 mm hohlraum and 1.0 mm×2.1 mm hohlraum is around 50%—55%.