Based on the baseline PI control structure, the control parameters of non-linear ALSTOM gasifier benchmark problem are optimized. Firstly, taking all the input and output limits under three load conditions as constraints, the relative IAE indices at six scenarios are calculated and optimized by using multi-objective optimization algorithm NSGA-II. A set of non-dominated solutions are obtained which facilitate the further improvement on the performance under coal quality change. Then among those non-dominated solutions, the solution with best coal quality flexibility comes to the fore through a selection procedure. The simulation results show that the optimization and selection procedure presented in this paper improves the baseline PI control performance with better dynamic responses and coal quality flexibility.