Abstract: In order to accurately calculate the deviation coefficient of natural gas in a high-CO₂ gas field in East China Sea, and further to improve the reliability of gas reservoir engineering, gas production engineering and surface engineering design, 192 groups of the high-CO₂ content gas deviation factor experiments were carried out with the Canadian DBR-PVT instrument. Then 192 sets of corresponding simulation calculations were carried out using 12 state equations such as BWRS, PR and SRK in ASPEN HYSYS software. The main influencing factors of the deviation factor were discussed, and the accuracy of calculating deviation coefficient by software state equations was evaluated. The results show that within the experimental range, pressure and CO₂ content have great influence on the deviation factor, while temperature has little influence on it. The deviation coefficient first decreases and then increases as the pressure rises. The PR and Sour PR state equations have the highest accuracy in calculating the high-CO₂ content gas deviation factor, with the average relative error of 1.09% and the maximum relative error of 5.74%. Therefore, when the CO₂ content of natural gas is high, it is recommended to use the PR and Sour PR state equations to calculate the deviation factor.