Objective To study the effect of corrosion inhibitors with various concentrations on X70 steel corrosion in multiphase flow state, especially under plug flow conditions. Methods The CO2 corrosion state of X70 steel under the condition of plug flow was simulated by using the self-made experimental device. The surface morphology and corrosion rate were observed and analyzed by electron microscopy and weight loss method. And numerical simulation was conducted to study the influence on CO2 corrosion rate of X70 steel of corrosion inhibitor glycol in the multiphase flow state. Results The coupon surface morphology and weightlessness rate of using homemade experimental apparatus was similar with using real ring test. The uniform corrosion inhibition efficiency was obviously improved when the corrosion inhibitor concentration was more than 35 mg/L. If corrosion inhibitor concentration was continuously improved, uniform corrosion inhibition efficiency would have no big change. Under multiphase flow conditions, effect of corrosion inhibitor on local corrosion was not obvious. The simulation results were similar to the experimental results when the corrosion inhibitor concentration of ethylene glycol was of up to 250 mg/L. Conclusion Homemade experimental apparatus can simulate gas-liquid two phase flow in the rolling pipeline, and the experimental results are reliable. There is critical concentration for best corrosion inhibitor efficiency. If it is less than the critical value, the corrosion inhibitor will have little effect on metal; if it is more than the critical concentration, the changing of the corrosion rate will be small. Under plug flow conditions, the corrosion inhibitor has impact on uniform corrosion only, but has small impact on local corrosion and even promotes the development of the local corrosion.