Abstract: In order to solve the serious corrosion of carbon steel welded joint in the ammonium sulfite during papermaking process, the corrosion behavior of the carbon steel welded joints, adopting shielded metal arc welding with J422 dectrode, TIG welding and CO₂ gas shielded arc welding, has been studied by three electrode electrochemical test and metallurgical structure analyses.The results show that the polarization curve of the Q235 steel joint welded by CO₂ gas shielded welding process in the 5%-11% ammonium sulfite at 20-80℃ is quite similar to the one of the base alloy, i.e. the two curves is close to each other, which means this kind of joint has the best corrosion resistance.The microstructure of Q235 steel joint welded by CO₂ gas shielded welding shows that the welded joint structure is consisted of massive amounts of pearlite and acicular ferrite, in which the fine perlites are dispersed in the ferrite.