The accidental release is one of the main risks during the pipeline transportation of supercritical CO2 for carbon capture and storage and enhanced oil recovery. The leakage of high pressure CO2 involves complex phenomena, including the expansion and flashing of the CO2 jet, dispersion of a dense CO2 cloud, falling of the solid CO2 and sublimation of the dry ice bank, as well as changes of pressure and temperature in the pipelines. A new experimental setup is developed to study the leakage behavior of high pressure CO2 flow in a circulation pipeline system, which is about 23 m long. The inner diameter of the pipeline is 30 mm. The pressure in the pipeline can be as high as 12 MPa with a maximum temperature of 50 °C through a high pressure pump and an electrically heated cloth around the pipeline. In addition, the velocity of the CO2 flow in the pipeline can be controlled in the range of 0–5 m/s by a circulation pump. The opening and closing of the small leakage hole can be remotely controlled by an operator. Pressure sensors are located nearby the leakage hole in the experimental pipeline system to monitor the pressure change during the CO2 leakage. Moreover, thirteen thermocouples are used to measure temperatures of the CO2 flow inside the pipe and on the surface of the pipeline. The experiments carried out show the typical characteristics of the supercritical CO2 flow leaked from a small hole.