A magnesium battery electrolyte with a wide electrochemical window was developed. The electrolyte includes an organic boron magnesium salt and an aprotic polar solvent. The organic boron magnesium salt is an organic boron magnesium salt complex formed by compounding a Lewis acid with a boron center and a magnesium-containing Lewis base R′2-nMgXn, wherein n is 0 or 1, R and R′ respectively represent a fluoroaryl group, an alkylated aryl group, an aryl group, an alkyl group, or a pyrrolidinyl group, and X represents a halogen. The solvent is an aprotic polar solvent such as ether or a mixed solvent thereof. The concentration of the electrolyte is 0.25 to 1 mol/L, and the electric conductivity is 0.5 to 10 mS/cm. The electrolyte allows reversible deposition/dissolution of magnesium, features good cycling stability, and has a wide electrochemical window (>3.0V vs. Mg/Mg2+).