Based on the friction stir welding rig，the temperature field model was established by FE software COMSOL Multiphysics under the coupling effect of Joule heat and friction heat. The coupled temperature field distribution and variation rule of the analysis model were simulated and analyzed under current carrying or not. The results show that, under the condition of without current carrying, the maximum temperature mainly distributes on the contact area of the pin tool and work piece, the temperature distribution area in front of work piece is larger than that in the rear, the theisothermal layer distribution of the front gets sparser compared with the rear，and the welding temperature gradient of the rear side is greater than that of the front. Under the condition of current carrying，the temperature distribution and isothermal layer with current is basically the same as that without current. The temperature distribution area of shoulder with current is greater than that without current. Under the constant welding velocity，axial force，rotation velocity and displacement，the maximum temperature produced by coupling function of Joule heat and friction heat is much higher than that produced by friction heat. The axial force required in the same heating efficiency is greatly reduced under the condition of current carrying.