Abstract: In the process of CO₂ pipeline transportation, water content is an important factor affecting the corrosion rate of the pipelines. In order to ensure safe operation of pipelines, therefore, water content of CO₂ shall be calculated accurately. In this paper, two different methods for calculating the water content of pipeline CO₂ were put forward, i.e., the simplified thermodynamic model and the empirical formula based on experimental data fitting. In the simplified thermodynamic model, the related physical parameters are calculated by the Peng-Robinson state equation and the CO₂-H₂O two-phase system is described by means of ϕ -γ method. And in the empirical formula method based on experimental data fitting, the empirical formulas for calculating the water content of pipeline CO₂ in gaseous and supercritical states are fitted with existing experimental data. It is verified by comparing with the actual measurement data in the existing literatures that average errors of calculation accuracy of the two methods under the condition of pipeline transportation are 1.40% and 6.69%, respectively, so both methods can satisfy the engineering calculation requirements. Finally, the application scope of two methods was proposed based on the error analysis results. The research results are of great significance for the operation management of pipeline CO₂ and the design of upstream treatment process.