The flow and filmforming characteristics in a horizontal rotating disk reactor have been numerically simulated by using the volume of fluid (VOF) model and were validated using experimental data from the literature. The effects of varying the rotation speed and liquid height on the thickness and distribution of the film thickness were also investigated. The results showed that the liquid flow field, the film forming process, the thickness, and distribution of the film thickness predicted by the VOF model are in good agreement with the experimental data. The thickness of the film increased as the rotation speed was increased, whereas the height of the liquid had little influence on the thickness of the film. A minimum rotation speed and liquid height were founf to be required for film formation. The distribution of the film on the surface of the disk was also obtained. The results are of importance for the design and optimization of rotating disk reactors.