Effect of cryogenic treatement temperature to corrosion behavior of AZ31 magnesium cold metal transfer(CMT) weld joint was studied by adopting electrochemical method.Result was that compared to non-cryogenic joint,the corrosion resistance of joints that were cryogenic treated under -100℃/4h,-140℃/4h,-180℃/4h were increased to a different extent.With the temperature decrease,the corrosion resistances show a downward curve after the initial raise.Critical cause of this trend are the change of the size,quantity and distribution of the second phase caused by cryogenic treatment. The weld zone that was cryogenic treated under -140℃/4h shows the best corrosion resistance because the charge transfer resistance and corrosion product film resistance of that reaches maximum and the corrosion current of that reaches minimum.