The phase equilibria and compositions in Mg-rich comer at 300℃ were determined in the Mg-Zn-A1 ternary system through the equilibrated alloy method by using X-ray diffraction (XRD) and scanning electron microscopy (SEM) assisted with energy dispersive spectroscopy of X-ray (EDS). The results show that there exist three three-phase regions consisted of a-Mg+Mg17A112(7)+A15Mg11Zn4(φ), a-Mg+Mga2(Al, Zn)49(r)+A15MgllZn4(φ) and a-Mg+MgZn+Mg32(A1, Zn)49(r), respectively. The intermetallic compounds in equilibrium with a-Mg phase all have large composition ranges, not appear to be linear. At the same time, both zinc and aluminum are soluble in the a-Mg solid solution, with which the compounds are in equilibrium.