Abstract: The modeling of industrial semi-batch stirred ethoxylation reactor was developed by taking ethylene glycol ethoxylation process catalyzed by KOH as example. The model took the kinetics, vapor-liquid equilibrium, vapor-liquid mass-transfer, variation of reactive volume, as well as the effect of inert gas nitrogen on the reactor into account. Based on the developed model, simulations were performed to investigate the effect of ethylene oxide (EO) feed flow rate on the reactor performance, so as to obtain the suitable EO feed flow rate within safety limits. The simulation results provided the typical dynamic profiles of the reactor pressure, the molar fraction of ethylene oxide in liquid and vapor, as well as the ethoxylated oligomer distributions. Simulation results were compared with the industrial experiment data, which showed the reliability of the developed mathematical model.