Abstract: Different from other liquids, liquefied (or supercritical state) CO₂ is characterized by relatively low critical temperature and pressure, and consequently susceptible to gasification during transmission. By using HYSYS, physical properties of CO₂ have been analyzed. In addition, hydraulic and thermal calculations have been performed for CO₂ pipelines under various working conditions. Pressure-temperature (p-T) curves have been generated in accordance with calculation results to identify rules of changes and relevant influencing factors for pipeline-transmission CO₂ under super critical phases, high-density phases and general liquid phases. Calculation methods for allowable inlet pressures and temperatures of pipelines have been developed to provide theoretical foundations for pipeline design. Research results show that density is the fundamental factor that may affect pressure drop in pipeline transmission. At the same time, impacts of viscosity can be neglected. The key to avoid gasification of CO₂ during pipeline transmission is proper control over inlet temperature and pressure of the pipeline; in addition, the highest ambient temperature shall be taken as the design parameter for CO₂ pipelines.