In 2011, new primary standard apparatus of spectral radiance was setup at Changping campus of NIM based on high temperature blackbody BB3500M and double-grating monochromator of M207D. The temperature of the BB3500M was measured by a LP4 thermometer with uncertainty of 0.64 K at the temperature of 2980 K, which was calibrated by the Pt-C and Re-C fixed point blackbodies, and checked by a WC-C fixed point blackbody. The consistency of the temperature at 3021 K was better than 70 mK between NIM and VNIIOFI. The image of the measuring source was focused on the entrance slit of the monochromator with magnification 1:1. A mask was put in front of the entrance slit to limit the target spot size of the tungsten strip and the water-cooled aperture was 0.6 mm wide by 0.8 mm tall rectangle. The solid angle of spectral radiance measurement was approximately 0.008 sr. Uncertainty of spectral radiance scale realization was analyzed in this paper. The source of the uncertainty scale includes repeatability of the signal ratio of the blackbody and the transfer lamp, lamp alignment, temperature measurement of HTBB, non-uniformity of HTBB source, instability of HTBB source, correction of different size of source (BB and lamp), nonlinearity of the measurement system, current passed through the transfer lamp, wavelength error, polarization effects, bandwidth etc. The measurement uncertainty (k=2) of spectral radiance was 1.8 % at 250 nm, 0.90 % at 400 nm, 0.64 % at 800 nm, and 1.3 % at 2500 nm respectively.