Objective To conduct flow field simulation analysis on an 80-ton bubble column bioreactor for equipment improvement and fermentation efficiency enhancement.Methods Computational fluid dynamics is resorted to numerical simulation of gas-liquid two-phase flow in a bubble column bioreactor. Euler-Euler method and k-ε model are used to simulate the turbulence of gas-liquid two-phase flow. The population balance model (PBM) is coupled to predict bubble size. The flow pattern, liquid velocity, energy dissipation rate, gas holdup, and bubble size distribution inside the reactor are simulated. Based on the permeation model, the calculation is performed on the volumetric oxygen transfer coefficient (k_La) inside the reactor, and an analysis is conducted on the influence of different reflux angles and diameters of the reflux pipe on the reactor’s oxygen supply capacity.Results The reflux pipe significantly impacts the reactor’s flow field, and positively impacts the liquid velocity, energy dissipation rate, and bubble size. The volumetric oxygen transfer coefficient of the reactor reaches 1 093 h^-1. There is an interactive effect between the reflux angle and the diameter of the reflux pipe, with the optimal combination as a diameter of 150 mm and an angle of 45°. Under these conditions, the volumetric oxygen transfer coefficient reaches 1 428 h^-1.Conclusion The reflux pipe makes the bubble column reactor comparable to the stirred reactor of the same scale in terms of oxygen supply capacity, playing a crucial role.