Abstract: Dewing behavior on specimens during warming and wetting processes in a weathering test chamber was predicted by computational fluid dynamics (CFD), and corresponding experiments were performed for validation. The effects of specimen size and materials on the dewing behavior were examined. The results show distinct size effect and material effect on the time of wetness (TOW) in the weathering test of engineering materials/components, indicating that these two effects should be emphatically taken into account in evaluating the safety of materials/components. Through deliberating and optimized modeling, good agreement between numerical simulation results and test data was achieved, which demonstrates that numerical simulation can be conducted to predict the heat transfer behavior and water condensation tendency on engineering components in weathering test.