The dynamic response of heat sink in the measurement process by an absolute cryogenic radiometer is studied with the finite element method, the key factors affecting the equilibrium temperature of heat sink and the temperature variations under different heat sink structures are analyzed, and the thermal responses when 304 stainless steel, 6061 aluminum alloy, and oxygen-free high-conductivity copper are respectively used as thermal links are compared. The results indicate that, a heat link with low heat capacity and thermal conductivity is the first choice in the future of cryogenic radiometers. In addition, the equilibrium temperature of heat sink can be effectively controlled via suitable adjustment of the heat sink structure.