In order to study the effect of the second phase on the corrosion behavior of Mg-Zn-Zr alloy, using ZK60 as samples, the corrosion behavior and mechanism of magnesium alloy with different second phase content and distribution in 3.5%(mass fraction)NaCl solution were investigated by optical microscope(OM), scanning electron microscope(SEM)and energy dispersive X-Ray spectroscopy(EDS).Result showed that both the content and distribution of the second phase would affect the corrosion resistance, and the distribution of the second phase was the main factor.The corrosion resistance of the samples with dispersed second phase was better than that of the samples with continuous strip distribution.The main reason for the above differences was that they had different corrosion types: when the second phase was distributed continuous, the main corrosion type was galvanic corrosion; when the second phase distributed dispersedly, galvanic corrosion and chemical corrosion occurred alternately.