Basing on the CEL numerical simulation method, adopted by Pressure Independ Multiyield Material model, the welding temperature field for friction stir welding (FSW) process of 2A14 aluminum alloy at different rotating speeds and welding speeds was simulated by finite element method. According to the temperature distributions, the variation rule of pre-molten viscousness layer at the front of the rotating tool was analyzed. Compared the requirement of rheological layer with simulated thickness of pre-molten viscousness layer, joint quality under different welding parameters was predicted. Therefore, the reference of process parameters selection for 2A14 aluminum alloy FSW was proposed.