This paper used the finite elements method to establish two-dimensional axisymmetric thermo-mechanical coupling model in friction pull plug welding （FPPW）. The results show that temperature rising rate of the interface in the initial stage was higher than that in the quasi-steady stage， because of the loss of friction heat to external environment. The temperature of the plate was higher than that on the plug side and the friction heat concentrated on the plug easily. Due to the decrease of strength and deformation resistance with the increase of temperature and strain， the interface and flash of upper wall was formed preferentially. The material flow of the lower wall occurred when the material was fully softened. After the welding process reached the quasi-steady state， the stress of the interface was distributed as the compressive stress on the central and tensile stress on the side， which derived the forming of flash on the plate. The simulation results agree with the actual welds.