This paper was on the forming characteristics of AZ 31B Mg alloy in a combined forward–backward extrusion (CFBE) at warm temperatures. Both experimental studies and thermomechanical finite element analyses were performed. A finite element analysis model coupled with damage evolution was presented. Based on our previous work, the forward extrusion ratio, backward extrusion ratio, forming temperature, and punch speed were chosen as the most important process parameters. Two punch speeds of 2 mm/s and 20 mm/s were examined for the forming temperatures of 180 °C and 200 °C. Forward extrusion ratios were 2.25, 4.0, and 9.0, while backward extrusion ratios were 1.33, 2.16, 4.02, and 7.75. Effects of those parameters on the forming limit, deformation behaviors, extrusion load, and the mechanical properties of an extruded product were discussed in detail. [ABSTRACT FROM AUTHOR]