A precise and efficient 3D-FE model of the porthole extrusion process for AZ31 Mg alloy thin-walled tube, used to manufacture towers antenna in battlefield, was developed in the DEFORM-3D software environment. And the influencing laws of ram speed on the load, welding pressure and the peak temperature of billet at die export were investigated and revealed by comprehensive numerical simulations. With integrated consideration of the extrusion load, quality of welding area and surface quality of the extruded tube, it is proposed that the optimum ram speed range is about 3.5~7 mm/s for the extrusion of AZ31 Mg alloy thin-walled tube on a 2000 t extrusion machine