Abstract: In order to realize the minimum resolvable temperature difference(MRTD) test of infrared detector in outfield, the principle and process of MRTD were described. Combined with the technical means in the past, a set of infrared target system for outfield was designed. By using the blackbody as the target source, the difficulty of control was reduced; by using the rotating target wheel to switch different spatial frequencies, the size of the blackbody was reduced; by using the 2D regulating mechanism, the azimuth and pitch angle of the target could be adjusted manually. The infrared target system can change the temperature from 5 ℃ to 100 ℃, and the target surface temperature inhomogeneity is less than 1 ℃. It can provide 12 groups of MRTD test targets with different spatial frequencies. After the finite element analysis, it is proved that the whole system has good stability and can meet the needs of outfield MRTD test.