Molecular weight distribution (MWD) is essential for describing the microstructural quality of a polymer. However, most of the studies on MWD are limited to ideal reactors. Computational fluid dynamics (CFD) methods is a useful tool to deal with the nonideal reactors. Few studies on CFD have been extended to the simulation and optimization of polymer MWD due to the computational difficulties. In this study, a new strategy is proposed to simulate the spatial MWD for a type of nonideal reactors using the method of moments with interfacing to the CFD software. Subsequently, given a target MWD curve, process optimization is proposed to achieve the optimal operating conditions. The tubular and autoclave reactors of the low-density polyethylene process are demonstrated for the simulations and optimizations. The influences of the decision variables on the feasibility and objective function are also discussed. (C) 2017 Elsevier Ltd. All rights reserved.