The addition of Zn has a significant impact on the microstructure and mechanical properties of Mg-Gd-Y-Zr alloy. In particular, the evolution of the LPSO structure plays an important role in the application of high-performance magnesium alloys. To investigate the effect of Zn on the microstructure evolution and properties of the Mg-Gd-Y-Zr alloy, Mg-10Gd-4Y-0.5Zr-xZn(x=0, 1, 2, mass fraction, %) alloys with different Zn contents were prepared by extrusion. The microstructure of the as-extruded alloys was observed by OM, SEM, XRD and TEM, and the tensile properties at room temperature were tested. The results show that the as-extruded alloy without Zn consists of the α-Mg matrix and a small amount of the Mg-RE phase. With the addition of Zn, the alloy consists of α-Mg with lamellar 14H-LPSO in the matrix, linear flow 14H-LPSO at the grain boundary and the Mg-RE phase. The grain size of the as-extruded alloy continuously decreases and the effect of fine grain strengthening increases with increasing Zr content. As a result, the strength of the alloy increases, while the elongation of alloys increases primarily and then weakens with the addition of Zr.