The resist film formation process that occurs during the utilization of the spin coating technique was numerically simulated. The simulation considered both the liquid film and the atmospheric gases above the film by using a novel system of governing equations. A 2-D simulation with axisymmetric full governing equations for Newtonian PMMA-chlorobenzene solution was performed. From this result the variables' dependency on the radial coordinate was determined and dominant terms in the governing equations were identified. Based on this radial dependency the 2-D governing equations were successfully reduced to 1-D equations. Using these 1-D governing equations, extensive simulation was performed. The resulting final film thickness was then compared with the experimental results of W. W. Flack et al. (1984), and excellent agreement was observed. The detailed behavior of the film formation process, such as the solvent evaporation and the increase in solute concentration which was accompanied by a viscosity increase, was clarified by these simulations.