Abstract: Before cold extrusion T3 copper tube surface appears serious corrosion after soften anneal and pickling, which cause the whole products rejected. The reason and mechanism of the surface corrosion of T3 copper tube were researched by using chemical composition analysis, metallographic examination. By synthesizing various testing results and using the simulation testing, the results showed that under wet condition, the copper contacted with chlorides and ion to cause chemical and electrochemical corrosion, and the heating for anneal made the copper tube corrosion seriously.