Electrochemical corrosion of metal involves the coupling of electrode reactions on anode and cathode surfaces which are all non-linear process,and transfer process.Aiming at the potential galvanic corrosion effect between the base metal(BM),heat affected zone(HAZ),and weld metal(WM)at the welded joint of X60 steel,a mathematic model is established,which couples the non-linear electrode reactions and transfer process.By numerical calculation,the electrolyte potential distribution at the welded joint,the current density distribution on electrode surfaces and the distribution of electrode potential polarization values are obtained.The effect of area ratio of cathode and anode,a critical parameter influencing the galvanic corrosion,is also investigated.The results show that the direction of electric field in the electrolyte is from HAZ to BM and WM,and thus the corrosion of HAZ is accelerated.At the regions where different zones contact,the current density on the electrode surface is large,making these locations become the sensitive regions to suffer galvanic corrosion.The total current flowing through cathode surface increases with the area ratio of cathode and anode when the anode surface area is fixed.The increase part of the total current flows out through the added cathode surface.The anodic current density also increases with the area ratio of cathode and anode,but the rate of increase becomes slow as the area ratio increases.