Objective To study the effect of corrosion on pressure loss of long-distance CO2 pipeline at supercritical and dense-phase states. Methods Assuming that the surface roughness of new seamless steel tubes was 0.1 mm, that of mild corrosion seamless steel tubes 0.25 mm and that of severe corrosion of seamless steel tubes 0.9 mm, effect of corrosion on the pressure distribution of long-distance CO2 pipeline with different roughness conditions at supercritical and dense-phase states was simulated and calculated by HYSYS software combined with basic data like transmission capacity, tube length and ambient temperature. Then the regulations of distribution influenced by roughness conditions were summarized according to the results of pressure distribution. Results With increasing roughness, pressure loss in flow process of CO2 pipeline at supercritical and dense-phase states increased continuously. Transmission at supercritical state was more affected by roughness than that at dense-phase state. However, subject to height difference, the results changed to that pressure loss at dense-phase state was larger than that at supercritical state. Conclusion Surface roughness has great influence on pressure loss of CO2 pipeline at different phase states. The pressure loss will increase for 9%~11.2% for every 1 mm roughness increases. Under the conditions without height difference, pressure loss at supercritical state is greater than that at dense-phase state. Subject to height difference, that at dense-phase state is bigger than that at supercritical state. For actually used pipelines, pressure loss at dense-phase state is larger than that at supercritical state.