Aiming at the problems of low strength and poor plasticity of magnesium alloys at room temperature, Mg-4Sn-2Al-1Zn alloys were extruded at 250℃ by compound extrusion process, and the microstructure evolution, texture and mechanical properties of the alloys after extrusion were studied. The results show that the grain size of Mg-4Sn-2Al-1Zn alloy can be refined from 45.2mm to 3.1mm by one-step compound extrusion, and the structure is uniform. The hardness and uniformity of the extruded alloy increased, and the yield strength, tensile strength and elongation after fracture were 204 MPa, 287 MPa and 21.0%, which were 140.0%, 91.3% and 156.1% higher than that of the homogeneous state, respectively. Dynamic recrystallization is the main mechanism of grain refinement. Grain refinement and basal plane texture enhancement after extrusion, and the texture expands uniformly in the extrusion direction improves the strength and plasticity of the alloy, and the Mg2Sn phase breakage further improves the mechanical properties of the alloy during extrusion. The above studies show that compound extrusion is a process that can effectively improve the comprehensive properties of magnesium alloys.