Abstract: The condensation phenomenon is very common in the thermal cycling test of aerospace electronic products. Undesirable damage of some electronic products would be caused during the test without dehumidification measures. In this paper, the causes of the condensation in the thermal cycling test are analyzed, two methods of dehumidification are proposed, namely, the use of the evaporator, and the nitrogen filling method, and they are validated by designed tests. It is shown that the dehumidification effect of the evaporator is not satisfactory in view of the significant increase of the relative humidity and the moisture content in the heating stage; while the more effective dehumidification method is to fill the nitrogen in the normal temperature stage to reduce the relative humidity before carrying out the test.