Abstract: In order to ensure the safe operation of pipelines in the process of CO₂ transportation, it is necessary to predict accurately its throttling characteristics so as to prevent the freezing blockage inside the pipeline after the throttling. In this paper, the throttling effects and mechanisms of CO₂ at different states were analyzed from the view point of molecule. Then, a method for calculating the Joule-Thomson coefficient of pipeline CO₂ was put forward by means of multivariate nonlinear regression method. In this calculation method, the formula for calculating the Joule-Thomson coefficient of pipeline CO₂ at three different states is developed with the advantages of simple form and quick calculation, so it is valuable in engineering application. Finally, the accuracy of empirical formula was verified using the experimental data. It is shown that under the operation mode of pipeline transportation, the average relative error is 10.63%. This calculation method can be used as the reference for the calculation of throttling temperature drop in the process of CO₂ pipeline design and operation.