Abstract: To determine impacts of foreign substances on orificing of CO₂ in pipeline transmission, CO₂ fluids containing foreign substances are studied to clarify method for calculation of temperatures after orificing with phase transition considered. Then, impacts of foreign substances on orificing of CO₂ in pipeline transmission are analyzed, and relevant operational procedures are proposed. Research results show that impacts of H₂S on temperatures after orificing are negligible. Within fluids at the inlet in super-critical, high-density or liquid conditions, SO₂ may effectively enhance temperatures after orificing, whereas nitorgen and oxygen may reduce temperatures after orificing. If fluids at the inlet are low-pressure gases, SO₂ may reduce temperatures after orificing, whereas nitrogen and oxygen may enhance temperatures after orificing. As for CO₂ with different contents of foreign substances, deviations in temperatures after orificing may vary from pure CO₂ gas. Generally, higher contents of foreign substances may lead to higher deviations. The research results may provide guidance for control over orificing of CO₂ fluids containing foreign substances and prevention of dry ice.