Blackbody radiation source as a primary standard, its measurement accuracy determines the uncertainty level of the whole traceability link. To improve the measurement accuracy of blackbodies′ radiance, a double-channel thermal-infrared standard radiometer was developed. According to the principle of the instrument, calibration coefficients of the standard radiometer were obtained by using a high accuracy water-bath blackbody. Experimental results suggest that the radiometer′s instability is less than 0.3% within one hour, uncertainty of fitting coefficient is less than 1.23%, and combined uncertainty is less than 0.39%, 1.3% in 5 μm and 10 μm channel respectively. This radiometer provides new means for tracing blackbody radiance directly to radiant standard in lab.