Abstract: To ensure the CO₂ transmission safety, a leakage and diffusion model for CO₂ pipelines was established using the software PHAST. In this model, the consequence of CO₂ leakage and diffusion is taken as the basis, and the phase change and gravity effect during CO₂ leakage and diffusion are taken into account. Then, the SLOD (death rate 50%) influence ranges at different valve spacing were calculated with the most unfavorable conditions as the initial condition, so as to determine the valve spacing of CO₂ pipeline in the areas of different levels. It is shown that for the sake of safety, a valve chamber shall not be constructed in level-one areas, but to carry out pipeline maintenance conveniently, a valve chamber can be installed in the location which is conducive to pipeline maintenance. The valve spacing in level-two areas can be selected according to the number of customers, but it shall not exceed 60 km. It is not recommended to conduct supercritical CO₂ transmission in level-three and level-four areas. To sum up, the study on the valve spacing of CO₂ pipelines based on the consequence assessment of leakage and diffusion provides some theoretical support for the formulation of specifications related with CO₂ pipeline transportation and the safety evaluation and accident consequence analysis on CO₂ pipelines in China.