With the new technology of large area high temperature fixed point, a 14 mm diameter WC-C high temperature fixed point blackbody source was established at NIM. National primary scales of spectral irradiance in the wavelength range from 250 to 2 500 nm, correlated color temperature and distribution temperature were realized at 3 020.11 K. This is the first time that the large area high temperature fixed point blackbody technology has been successfully applied to the field of spectral radiometry. A selective multiple fit methods for calculating the point of inflection temperature of fixed pointmelting temperature plateau was proposed to solve the fluctuation problems of large diameter fixed point blackbody temperature plateau curve. The Akima fitting method was used to restore the missing part of the melting plateau curve. Using a double grating spectral comparison measurement system, a halogen tungsten lamps realized and preserved the spectral irradiance scale. Measurement uncertainty of the temperature of the blackbody was reduced to 0.36 K using the new method, and the traceability chain was shortened. The best measurement uncertainty of spectral irradiance is 0.25% (k=2). Spectral irradiance was realized respectively based on fixed point and variable temperature blackbody, and the average divergence between the two methods is 0.42% from 250 to 2 500 nm. By combining the two methods based on fixed-point blackbody and variable temperature blackbody, the expanded uncertainty of spectral irradiance national primary scale was realized as 1.9% at 250 nm, 0.43 % at 400 nm, 0.25% at 1 000 nm, 0.76% at 2 200 nm, and 2.4% at 2 500 nm respectively. The spectral irradiance scale realization technology based on fixed point blackbody has been applied to improve the calibration accuracy of the remote sensing spectroradiometers.