A hot air drying technique, which is widely used in the production of coating materials, was studied by using experiments and numerical analysis about the surface liquid flow and the evaporation rate. The influence of liquid surface flow on the drying rate was investigated by experiments on liquid film of 100 mm square and of 0.2 mm thickness, and the influence was found to be very small. Based on the result, we proposed a formula for estimating the evaporation rate of water by utilizing a well-known theoretical formula of mass transfer with a modifying factor. In order to predict the time-dependent change of the drying rate, it was necessary to consider the diffusion of water inside the liquid film, as it was the rate-determining process. A one-dimensional numerical model was utilized for analyzing the water transport and the time-dependent evaporation rate, and reasonable agreement with the experimental data was successfully obtained.