Abstract: The corrosion behavior of high frequency resistance welding (ERW) joint of Q125 grade tube steel was studied by SEM,EBSD and electrochemical measurement under CO₂/ H₂S environment. The results showed that the corrosion prosperty of joint was worse than that of the base metal and heat affected zone,thus the grooving corrosion occurred in the ERW welding joint under CO₂/H₂S environment. The proportion of large-angle grain boundary in welding zone was more than that of base metal and heat affected zone,which played an important role in the highest corrosion rate of welding zone. Electrochemical analysis results demonstrated that welding zone was easy to corrode because of its smallest polarization resistance in electrode reaction, while the polarization resistance of base metal was the biggest. All of these were consistent with the result of corrosion test and analysis of polarization curve.