Abstract: There is little research on how the flow parameters of CO₂ pipeline vary during its venting, and the related codes have no definite requirements on venting. In this paper, the particularity of CO₂ pipeline venting was analyzed, and the effect of delivery pressure and discharge rate on the venting characteristics was calculated after the mathematical model was established for the transient process inside pipelines. It is indicated that the remaining CO₂ in the pipeline is the power function of time. The venting time becomes longer in high pressure and low temperature. The joint "convergence zone" of all phases of CO₂ appears during the venting. The venting characteristics of dense phase CO₂ are similar to that of liquid CO₂. Dry ice may generate in the process of supercritical venting. And the venting rate has less influence on the temperature drop inside the pipeline, however, the lower discharge rate can cause slower temperature drop. Therefore, it is recommended to slow down the opening rate of vent valve and heat the vent pipe locally so as to protect the equipment and prevent dry ice blockage. The research results provide references for designing CO₂ pipeline venting plan and drawing up the related codes.