An accurate modeling method is proposed for the infrared characteristics of space target. Fully considering the heat conduction among the surfaces and the effect of inner heat source, the heat balance equation is presented for space target in the background radiation environment, and on the basis of structural and material properties of the target, the temperature distribution of target surface is calculated by node network method. According to the optical radiation and scattering theory, the mathematical model on infrared characteristics of space target is established and the general calculation method for infrared characteristics of space target is derived. Finally, the temperature field and irradiation distribution of ZY-1 and FY-3 satellite are computed using the given parameters. The computation results illustrate the validity of the theoretical analysis.