For determining the corrosion behavior of L320 steel at different flow rates in CO2/O2 environments, the flow state of the target pipeline was simulated through the multiphase flow transient simulation software, and the flow velocity range of the indoor simulation experiment was determined. The L320 steel was selected for the high temperature and high pressure dynamic reactor experiment with different flow rates under the CO2/O2 coexistence systems, and the corrosion products were studied by scanning electron microscope and X - ray diffractometer for the microscopic morphology observation and composition analysis. Results showed that the temperature and pressure showed a downward trend with increasing mileage, and the gas flow rate and wall shear force of the pipeline exhibited a gradually increasing trend with the increase of the mileage. Based on the Pearson correlation coefficient method, it was determined that the flow velocity was the main controlling factor affecting the corrosion rate. With the increase of flow rate, the uniform corrosion rate of L320 under the condition of CO2/O2 coexistence gradually increased. The corrosion products of the CO2/O2 coexistence systems were Fe2O3, FeOOH, Fe(OH)3, Fe3O4, FeCO3, etc. The research conclusions could provide reference for the protection of L320 steel in CO2/O2 coexistence environment at different flow rates.