Abstract: Lowtemperature infrared radiators have been used widely with the rapid development of space infrared detection, satellite remote sensing. One kind of lowtemperature infrared radiator based on liquidcirculation temperature control was developed. The range of radiant temperature for this radiator is -60 ℃~50 ℃，the temperature control accuracy reaches 0.01 ℃, and the effective emissivity is better than 0.999 7. First, the design principle of this radiator was described, and the structure characteristic for the radiation cavity was depicted, the calculation by using STEEP3 software based on the MonteCarlo algorithm for emissivity was also given. The temperature characteristic for inner part of radiation cavity was then studied, the temperature uniformity of the inner cavity verified by valid testing was better than 0.02 ℃, the temperature stability for bottom of cavity was 0.05 ℃/h. Finally, the normal spectral emissivity of the radiator at the temperature of 29.76 ℃ was obtained by comparing its radiance with a gallium melting point blackbody, the experimental value was the same with the result calculated by STEEP3.