Abstract: The fundamental forming process of friction stitch welding is friction hydro pillar processing, which is the key process that effects the quality of Friction Stitch Welding.A three-dimensional thermal mechanical coupling model of FHPP process was established by using finite element code MSC.Marc.The calculated results with material coupling of Q235-Q235 indicate that the temperature distribution on the friction surface has a tendency to rise gradually from the inside to outside on radial direction during welding process, while the contact pressure distribution decreases gradually. With the increase of rotary speed, the temperature is remarkably increased while the material doesn't illustrate obvious plastic deformation, but the effect is relatively weak with the increase of temperature.When material in the contact zone illustrates plastic strain at high temperatures, increasing axial force is more effective for increasing temperature and inducing large deformation.