The numerical model was established to simulate the 30 mm-thick bobbin tool friction stir welding process,which calculated the temperature field and flow field of two different bobbin tools. It is implied that the high temperature area is near the shoulder,which reduced along the depth to the central plane of the thick plates. The temperature in retreating side is higher than the advancing side. Using the cone-shape probe caused higher temperature than cylinder-shaped tool. It is indicated that material near the FSW shoulder flows more fiercely than inside zone. It flows more turbulently using the screw thread structure than the parallel-grooves probe,which is coincide with the weld shape results.