A modeling method of infrared dynamic radiation characteristics of the space target was presented. Infrared radiation of the target consists of self-emitted infrared radiation and reflected background infrared radiation. A physical model of radiation characteristics of the space target was established according to target and background characteristics. The target surface was divided into regions and grids based on material properties. According to thermal equilibrium equation of outer space target, a mathematical model on infrared radiation characteristics of the space target was presented based on conservation of energy principle. Bidirectional Reflection Distribution Function (BRDF) was introduced to describe infrared reflection characteristics of the target surface element, and a mathematical model on infrared reflection characteristics of the target was built by superimposing all the reflection components of surface elements. Finally, a body coordinate system was set and the relative positions of the target, the background radiation sources and the detector were determined in terms of coordinate conversion. Simulation of the target infrared characteristics in orbit was achieved according to its given orbital parameters, physical dimension and physical parameter of the target. The calculations show the model is valid and it can provide reference data to visible detection and recognition of space targets.