Magnesium alloys are widely used in aerospace, automotive, digital and other important fields due to their low density, high specific strength, and good electromagnetic shielding properties, but their poor corrosion properties limit their applications. The crystol structure of rare earth elements is the same as that of magnesium alloys, and have a large solid solubility in α-Mg, the formed intermetallics second phase can refine grain size, and rare earth element can chage the microstructure fo corrosion layer, thus effectively improving the corrosion performance of magnesium alloys. In this paper, the corrosion rate and microstructure after corrosion of the Mg-3.4Y-3.6Sm-2.6Zn-0.8Zr alloy were characterized by X-ray fluorescence spectrometer, optical microscope, scanning electron microscope, electrochemical station, AFM test and other test equipments, and the influence of precipitation on the corrosion behavior of rare earth magnesium alloy was studied. The results show that rare earth elements Y and Sm form two precipitat (Mg,Zn)3(Y,Sm) and Mg12(Y,Sm)Zn in magnesium alloys. During the corrosion process，the (Mg,Zn)3(Y,Sm) phase is etched first, followed by the α-Mg matrix and the Mg12(Y,Sm)Zn phase. The precipitates form a corrosion product film during the alloy corrosion process, which increases the electrochemical impedance spectrum resistance value of the alloy. The corrosion product film protects the alloy and effectively reduces the corrosion rate.