Abstract: The dispersion laws of medium volume fraction and the scope of hazardous area in the case of CO₂ pipeline leakage are the important parts in safety assessment of CO₂ pipeline. In this paper, leakage experiments were performed on CO₂ of gas phase, dense phase and supercritical phase at different discharge diameters by using an industrial scale CO₂ pipeline release experiment device of 258 m long, and CO₂ volume fraction in different points of dispersion area were measured. The maximum volume fraction of each measurement point was taken as the study object to analyze the change law of CO₂ volume fraction with the distance along the axis of release orifice and the distribution of CO₂ volume fraction in the dispersion area. It is indicated that CO₂ volume fraction in three phase states decreases exponentially with the increasing of distance along the axis of release orifice. If CO₂ volume fraction is set at 1%, the hazardous distance along the axis in three phase states is about 30 m for the discharge diameter of 15 mm and 40 m for that of 50 mm. Considering the factors of wind velocity, land form, testing error and etc., it is appropriate to set two times of safety allowance as the safety distance. The research results can be used as the reference for the setting of safety distance in the process of industrial application.