In order to meet the requirements of long and highly precise heat flux measurement under laboratory conditions, a new radiative heat flux meter was developed based on the principle of electrical substitution measurement. The radiative heat flux meter can be traced to the International System of Units through self-calibration. Firstly, the system structure of the radiative heat flux meter is briefly described. Combining with the measuring principle of the radiative heat-flux meter, the measurement uncertainty of nine uncertainty components and their combined standard uncertainty in the process of radiative heat-flux meter self-calibration are analyzed and calculated. Then, the uncertainty of a radiometric heat-flux meter is verified by direct comparison with a standard detector calibrated by the National Institute of Metrology of China. Finally, according to the experimental data and analysis results, this paper provides a reference for the optimization design of the heat-flux meter. The experimental results show that the relative standard uncertainty of the radiative heat-flux meter is better than 0.26%, and the normalized error is 0.60, which verifies the validity of the uncertainty evaluation results. The experimental results will guide the development of radiative heat flow meters in the next stage and further improve its performance.