The extrusion experiment at different extrusion parameters was studied, the effect of the different extrusion parameters on the microstructure and mechanical property of Mg-4.8Zn-1.2Y-0.4Zr magnesium alloy was described, based on the experimental results and analysis. The result shows that dynamic recrystallization has been observed after the hot extrusion process, the alloy grain which compares with as-cast alloy is refined. The phase of extruded alloy is W-phase, there is great morphology and distribution difference during different extrusion parameters. The microstructure and mechanical properties of magnesium alloy was affected by extrusion temperature and extrusion ratio during the hot extrusion process. When the extrusion ratio is the same, the number of recrystallization grains increases with the increasing of temperature, meanwhile recrystallization grains also has a tendency to grow up.When the extrusion temperature is 300 ℃, the comprehensive mechanics performance of alloy is the most excellent. The influence of extrusion ratio on the plasticity of the alloy is obvious, when extrusion ratio is 25, the alloy elongation of alloy increases significantly.