The hydrostatic extrusion process of magnesium alloy AZ80 tube with different mandrel angles (90°,120°,150°) was simulated by the DEFORM-3D software with different extrusion speeds and initial billet temperature. The simulated results show that the peak load of the extrusion process with big mandrel angle is obviously higher than that of the small angle and the inhomogeneity of billet velocity field is intensified with the increase of the mandrel angle.