A computational model was introduced to study the effect of fuel mixing in waste bed combustion in municipal solid waste incinerators. One-dimensional progress of the apparent flame zone into the bed was simulated by accommodating the heat and mass transfer, along with heterogeneous combustion and gaseous reactions in the waste bed. Mixing of the waste bed was modeled as an exchange of certain sections in the fuel layer from a cold region over a flame region. Combustion characteristics of the waste bed based on the model prediction are discussed, along with the experimental measurement results from a batch-type bed reactor. The computational model adequately described the heat transfer of the unburned fuel section over the existing flame zone. Improvement of the combustion intensity by fuel mixing was observed, as evidenced by a decrease in the required time for complete burn-out. Control of the primary air supply could further enhance the waste combustion, which is a common practice in commercial incinerators.