The degree of desulphurization was studied using response surface methodology (RSM), which enables effect examinations of parameters with a moderate number of experiments. All experiments were conducted in a lab-scale spray tower for limestone/gypsum wet flue gas desulphurization (FGD). The model flue gas was prepared from air and SO2 gas. The SO2 concentrations in the gas phase were determined by a multi-method analyzer. The degree of desulphurization correlated well with operating parameters, including pH, L/G, T, and v, with a determination coefficient R-Sq of 0.964. Effect tests indicate that L/G has the most significant influence on the degree of desulphurization. The interactions of L/G with pH, and with v, both play important roles. The result indicates that the evolutive response surface model is helpful to describe the degree of desulphurization of the limestone/gypsum wet FGD spray tower.