The invention discloses an electrolyte of a magnesium air battery. The electrolyte is a buffer solution system formed by acetate and acetic acid, wherein the acetate is one or multiple of magnesium acetate, calcium acetate, barium acetate, strontium acetate, sodium acetate, potassium acetate and lithium acetate. Compared with the prior art, the electrolyte provided by the invention has the advantages that the performance degradation of the electrolyte is relatively slow in the using process, and the electrolyte regeneration can be realized, so that the maintenance period of the magnesium air battery is prolonged.