The absorption cavity module is an important component of the electrical substitution cryogenic radiometer. When the cryogenic radiometer works, the absorption cavity and the thermal link jointly establish and maintain the thermal balance. According to the measurement principle of electrical substitution, the equilibrium state of light radiation heating and the equilibrium state of electrical substitution heating were established, respectively. In order to accurately describe the differences of temperature distribution and electrical substitution inequivalence between the two equilibrium states, the differential heating method and finite element simulation method were proposed to evaluate the inequivalence caused by heating paths. According to the results of simulation analysis and uncertainty analysis, the difference of temperature measured by heating path is 1.5×10^?5 K, and the inequivalence of electrical substitution heating is 1.2×10^?8 W.