A mathematical model of the absorption of HCl gas-in a spray dry tower has been proposed. The proposed model describes the mechanism of HCl removal taking into account the atomized droplet size distribution and the change in the droplet state from ＇＇slurry droplet＇＇ to ＇＇dry particle＇＇. It is found that the removal efficiency can be simulated by using the model with the constant mean diameter of droplet from the simulation results. Simulation results of the removal of HCl gas are in good agreement with the experimental data in a spray dry tower.