Mg-4.8Zn-0.8Y, Mg-18Zn-3Y, Mg-15Zn-5Y, Mg-30Zn-5Y and Mg-42Zn-7Y (wt%) alloys containing icosahedral quasi-crystalline phases were prepared using the ordinary solidification method. The impact of Mg matrix porosity on the tensile strength and hardness of the alloys was studied. The porosity of the Mg matrix was quantitatively assessed using scanning electron microscope and Image-Pro Plus 6.0 software. Tensile tests were conducted at room temperature. Results show that the maximum tensile strength of the alloy is 175.56 MPa, with a corresponding Mg matrix porosity of 76.74%. Through fitting analysis, it is determined that the maximum tensile strength is achieved when the porosity of the Mg matrix is 64.87%. The microhardness test results indicate a gradual decrease in alloy hardness with increasing the porosity of Mg matrix. This study provides an effective quantitative analysis method for enhancing the mechanical properties of magnesium alloys.