Friction stir welding of 10 mm T2 cooper with different process parameters were studied in this paper. The results showed that the defect-free sound joints with good surface forming can be achieved with in certain ranges of process parameters. The weld cross-section consists of weld nugget zone,heat affect zone and base metal,the thermo-mechanically affected zone was not found.Significant dynamic recrystallization occurred in the weld nugget zone and fine equiaxed crystal structures were obtained. The grain size in heat affect zone increased a little. The distribution of microhardness at cross-section was "W" shape. the microhardness values of stir zone and heat affected zone were lower than base metal the lowest microhardness occurred in heat affect zone,the microhardness in weld nugget zone were relative stable. The tensile strength of the joint reached 97% of the base metal,when the rotation speed was 400 r/min and the welding speed was 100 mm/min. The fracture positions of joints under different parameters were at the retreating side of the heat affected zone.