Abstract: In order to obtain the dynamic corrosion characteristics of 5Cr steel welded joints for fusion welding, the CO₂ corrosion resistance behavior of these joints was studied by using electrochemical method based on electrode potential. The corrosion model based upon polarization curve was established and the corrosion resistance of welded joints with different fillers was studied. It was found that under the accelerated corrosion conditions of temperature 40 °C and CO₂ partial pressure 10 atm, the corrosion potential of low-chromium welding wire was the most positive and the corrosion rate was the least. For high-chromium and non-chromium welding wire, corrosion potential was the more positive and the most negative, respectively. Then corrosion rate of non-chromium fillers was the highest. Compared with weight-loss method which only shows mass change before and after corrosion, the electrochemical method is concerned with the dynamic corrosion rate at any time of the corrosion cycle. The corrosion rate based on the electrochemical corrosion model showed good agreement with the results of the weight-loss method. The correctness of the electrochemical corrosion model is validated. The results showed that 5Cr steel welded joint with the match of suitable low chromium welding wire could have stronger CO₂ corrosion resistance.