Abstract: In the context of carbon peaking and carbon neutrality, the pipeline transportation of supercritical/dense-phase CO₂ is a vital link for achieving carbon capture, utilization, and storage (CCUS) technology. In the process of actual transmission of the pipeline, affected by gas purification costs and external environment and other factors, there may be a certain amount of water inside the CO₂ pipeline, and the small rough structure on the surface of the pipeline may cause water to condense on the pipe wall, and even to form water droplets at low temperature, giving rise to an increase in the moisture content of local areas. H₂O reacts with supercritical/dense phase CO₂, SO₂, NO₂ and other acidic gases to form acidic substances, resulting in corrosion of the inner wall of the pipeline and threatening the its operation. The monitoring and control of water content of supercritical/dense phase CO₂ pipeline is the key to ensure the safe operation of the pipeline. However, the supercritical/dense-phase CO₂ environment is characterized by high pressure and trace water, which makes it difficult for traditional electrochemical testing methods to be applied to such environment, and it is urgent to develop water-content and corrosion behavior monitoring technologies suitable for supercritical/dense-phase CO₂ environment. A supercritical/dense-phase CO₂ water content monitoring technology based on in-situ electrochemical noise were developed. The corrosion behavior of X65 steel in supercritical/dense-phase CO₂ corrosion environment under different water content conditions was further studied in combination with corrosion loss experiment and surface analysis. By comparing and analyzing the difference of electrochemical noise under different water content conditions, the relationship between the characteristic parameters of electrochemical noise and water content was defined, and the monitoring method of water content was established. The critical water content in supercritical/dense-phase CO₂ environment was determined based on the specification of corrosion control in pipelines and electrochemical noise technology. The results show that there is a good correlation between the slope of the linear region of the PSD and the moisture content, and the electrochemical noise technology can be used to monitor the moisture content in the corrosion environment in real time. The error of the corrosion current density obtained by electrochemical noise was less than 14% compared with the corrosion rate measured by experiment. On this basis, combined with the code for internal corrosion control, the requirements of supercritical/dense phase CO₂ pipeline for water content control were proposed, which were 780 ppmv and 350 ppmv respectively. In this study, the real-time monitoring of water content in corrosion environment was realized by in-situ electrochemical noise measurement technology, and the control standard of critical water content was put forward, providing valuable guidance for field technology application.