Abstract: Quantitative measurement of fluid film flow is a necessary means to analyze the heat transfer process of the icing phase change. Digital Image Projection (DIP) based on image processing enables non-invasive quantitative measurement of fluid films. Firstly, the basic principles, cross-correlation algorithm and calibration method of the DIP technology are introduced. Based on this, the DIP system and the flat water film flow test bench are designed and built. Subsequently, the overall error of the DIP system was tested and was found to be within 5%, indicating the reliability and accuracy of the system. A series of water film flow experiments were carried out on a flat water film flow test bench. The DIP system was used to restore the three-dimensional full picture of the flat water film flow. Finally, the relationship between the average water film thickness as well as the dimensionless water film thickness and the water film Reynolds number is obtained by fitting the measurement results, and is compared with the theoretical derivation and literature experimental results. Results show the overall trend is consistent.