Abstract: Friction stitch welding is a new kind of solid phase joining technology, it has been less than twenty years since the welding institute put forward this concept.Friction stitch welding consists of a series of friction hydro pillar processing (FHPP) intersecting with each other, either in the form of cylinder-type combination, or taper-type combination.It can be divided into three stages for each FHPP process, i.e., the touch-down conditioning period, the steady pillaring period and the forging period with no stud rotation. The main factors influencing the quality of friction stitch welding include stud rotating speed and axial force applied.There exist great differences from other friction welding processes in forming mechanism, such as friction plug welding, friction surfacing, friction plunge welding and soon.Because friction stitch welding can accomplish good bonding properties under the condition of dry or wet environment, it has great application potentials in material forming process, especially in the case of underwater repair for steel structure.