The invention relates to a target heat radiation analyzing method in a space environment simulating device. A space three-dimensional simulation scene is firstly established adopting a simulation method, and a heat effect model and a test target is included in the scene; then a heat equation of the test target is established according to determined heat effect model; then a working condition parameter is input, and solution is conducted on the heat equation; and a temperature field and an infrared radiation field of the whole scene are finally generated according to the solved equation. According to the target heat radiation analyzing method in the space environment simulating device, a large spherical vessel, a heat sink, a solar simulator, a background radiation simulator, a test track and device, a rotary table and an observation window simulation scene are adopted, radiation heat transfer analyzing is conducted coupling three-dimensional unsteady state, and thus radiation field with waveband of 30-50 mum can be accurately simulated.