The extrusion process and mold design of aluminum alloy profile with large section and complex shape were studied, based on the ALE FEM software HyperWorks. The numerical simulation model of aluminum profile extrusion process was established, and an analysis was made on it to obtain the metal flow law of aluminum profile extrusion process. According to the simulation results, the paper analyzed the metal flow behavior of velocity distribution, particle trajectory, stress and strain distribution, which influenced by welding chamber of each layer height, shape and size and structure parameters of mold, and also optimized the structure parameters of the mold. Calculation results show that, the optimized mold can make the metal flow at the exit relatively uniform, and reduce the distortion degree of the product, which can meet the requirements of section shape and dimension precision of aluminum alloy.