Abstract: Mg-5.0Zn-xCa （x=0,0.25,0.50） alloys were prepared by metal mold casting.And homogenizing treatment and hot extrusion of the alloys were carried out.The effects of Ca on the microstructure and mechanical properties of Mg-5.0Zn-xCa alloy were investigated by OM,SEM,EDS and tensile tests.The results show that with the increase of Ca content,the Mg Zn phase in the as-cast Mg-5.0Zn-xCa alloy decreases gradually,the number and size of Ca₂Mg₆Zn₃ phases increase gradually,the grain size increases.The Ca₂Mg₆Zn₃ phase in as-cast Mg-5.0Zn-0.5Ca alloy presents a discontinuous network structure.The grain of extruded Mg-5.0Zn-xCa alloy can be refined obviously by adding Ca element.With the increase of Ca content,the grain size of extruded Mg-5.0Zn-xCa alloy decreases gradually,the strength increases gradually,and the elongation increases first and then decreases.Mg-5.0Zn-0.50Ca alloy has the best strength,and the Mg-5.0Zn-0.25Ca alloy has the best plasticity,and the elongation is 25.4%.