Under different conditions, the state of carbon dioxide is different. The starting point of pipeline transportation may be in liquid state or supercritical state. However, during pipeline transportation, the pressure and temperature will decrease with the decrease of pipeline length, and the phase state of carbon dioxide will change accordingly, which will affect the efficiency of pipeline transportation or cause serious pipeline blockage. In order to determine how much pressure to set at the starting point of pipeline and the length of pipeline section in the middle of compressor station, it is necessary to know the density variation law of carbon dioxide in detail. Using Hysys process simulation software, the density of pure carbon dioxide changes with pressure under P-R model as shown in the following figure.