The flow pattern in a rotating packed disk reactor was studied by using dye tracers in 50% glycerin solution. Based on the observation it was postulated that the fluid can be divided into two regions of mixing one region where fluid rotates in the same direction of the disk, and the other region where fluid rotates in the opposite direction. The fluide in the two regions were highly turbulent and perfectly mixed. A three-parameter multi-step model was adopted, with each step composed of two perfect mixing regions and a bypassing to illustrate the residence time distribution of fluid in the reactor. The parameters of the model were obtained from the experimental data, using Marquardt’s optimization algorithm. The model was in good agreement with the experimental data. Correlations were proposed for the analysis of residence time distribution.