The invention discloses a Zn-Mg zinc alloy and a preparation method and application thereof. The zinc alloy contains Zn and Mg; and the weight percentage of Mg in the zinc alloy is 0-20%, 0 not included. The zinc alloy further contains microelements which are at least one of strontium, calcium, silicon, phosphorus, lithium, silver, tin and rare earth elements; and in the zinc alloy, the mass percentage of the microelements is 0-3%, 0 not included. The mechanical performance of the Zn-Mg zinc alloy accords with the strength and toughness requirements of a medical implant material; the Zn-Mg zinc alloy is non-toxic, has excellent histocompatibility and blood compatibility, and can be degraded in vivo; and metal ions obtained from dissolving can be absorbed and used by living bodies to promote bone growth, or can be removed from the bodies through metabolism.