A method was presented to predict phase change behavior and liquid film evolution on specimens by combining the Eulerian wall film (EWF) model of two-phase flow with the self-defined formula of dew amount. Firstly, a self-built environmental test chamber was used to carry out condensation physical tests, and simulated tests were respectively performed based on the EWF model and the single-phase flow model. It is found that the EWF model is more accurate than the single-phase flow model due to necessary consideration of the phase change process. Then, a self-defined formula was established to calculate the dew amount and it was verified by the physical tests. Finally, under the premise that simulated and tested temperatures, relatively humidity curves and dew amounts show good agreement, the changing process of liquid films on specimen surfaces was predicted, and the simulation prediction of liquid film shape on specimen surfaces is in consistent with in-situ video imaging morphology during the physical tests.