For aluminum profile with non-symmetrical section, large wall thickness and complex hollow section, it is difficult to balance the metal flow during the conventional porthole die extrusion process, and bending and twisting may occur in the extruded profile. Therefore, adding the pre-dividing porthole die before the conventional porthole dies was put forward, and the traditional three stage of dividing-welding-forming was changed into four stage of pre-dividing, dividing, welding and forming so as to balance metal flow velocity. The results show that the metal flow uniformity is improved by the double stage porthole die compared with the conventional porthole die extrusion, and the mean velocity of metal flow in each hole is 6.41 mm·s-1 and the variance is 0.2511, which is decreased by 65％. Meanwhile, the extrusion temperature field distribution is uniform, the temperature difference is between 7-12 ℃，which can offset the effect of temperature difference. Furthermore, the average value of hydrostatic pressure in welding chamber is about 290 MPa, and the distribution of the hydrostatic pressure around the mandrel is uniform and difficult to move.