The conversion rate of SO2 is of great significance to the efficiency of sulfuric acid production with flue gas. However, the existing optimization methods for SO2 conversion rate can hardly achieve the optimal effect, because the parameters change and the working conditions fluctuate during the production process. Therefore, we propose a modifier-adaptation strategy with regulatory factors for real-time optimization of SO2 conversion process in this paper. We first establish the optimization model of converter inlet temperature. Then, considering that the plant-model mismatch during the process of sulfuric acid production with flue gas is mainly caused by the change of initial oxygen concentration, initial SO2 concentration, gas flow rate, catalyst activity and other factors, we study a modifier-adaptation strategy for real-time optimization with regulatory factors, designing and ameliorating the modifier term. We use the measurement values and gradient information in the real industrial process to revise the original optimization problem continuously, so that the solution will converge to the optimal set point of the real industrial process. The simulation results show that both the convergence rate of the proposed optimization strategy and the total conversion rate of SO2 have been improved. (C) 2017 Published by Elsevier B.V. on behalf of Institution of Chemical Engineers.