Abstract: By means of heat analysis and test of a typical device onboard spacecraft,a small scale heat balance test method was introduced to verify the device heat design,so that the repeated whole satellite's heat balance test can be avoided,and just need to verify the changed design of the key device.An equivalence radiation characteristic node and conductive characteristic node were presented to simulate the whole satellite boundary conditions in which the device existed.In addition,a revised model was introduced to analyze the errors resulted under the hypothetic boundary conditions.The rationality and limits of the method were dissassed,and suggestions in application were presented.