Bobbin tool friction stir welding is a new type of friction stir welding. In the study, the thermo-mechanical model of the bobbin tool friction stir welding was set up. By this model, the temperature field of AA 2014 aluminium alloy work plate of 6mm was simulated, which provides useful information for the investigation of this new process. Simulation results show that the temperature field of the cross section presents symmetry approximately about the mid thickness of the work plate. The high temperature zone has large radius at bottom and top surfaces near the shoulders while small radius at the mid thickness, like a waist. The max temperature for the point at retreating side is about 40°C higher than advancing side.