Abstract: Material flow in friction stir welding (FSW) of LF6 aluminum alloy and LD10 aluminum alloy was studied under different welding conditions. The research results showed that adequate plunge depth and push angle promote the metal plastic flow. The thread tool hardly affects metal flow in vertical direction. At the certain range, increasing spindle speed or welding speed of tool, vortex structures within welding zone appear to stable and well-distributed. When LF6 at retreating side, the combined interface of the two metals in low parameter is apparent, and the vortex structures had not been observed. By raising the parameters, when LF6 at advancing side, the vortex structure could be seen clearly regardless of whether the parameter are high or low.