The invention belongs to the technical field of metal materials, and particularly relates to a high-strength corrosion-resistant magnesium alloy and a preparation method thereof. The high-strength corrosion-resistant magnesium alloy is prepared from, by mass, 7.0-7.5% of Sn, 0.2-0.6% of Bi, 0.1-0.3% of Sb and the balance Mg and inevitable impurities. Components, including magnesium, tin, bismuth and antimony, of the high-strength corrosion-resistant magnesium alloy are smelted and cast to obtain as-cast alloy; then, heat treatment is performed on the as-cast alloy to obtain the high-strength corrosion-resistant magnesium alloy. The high-strength corrosion-resistant magnesium alloy has good room temperature strength and corrosion resistance, the tensile strength at the room temperature is higher than 270 MPa, and the corrosion rate in a 3.5wt% NaCl solution is lower than 0.6mm/a. Compared with commercial magnesium alloy AZ91, the high-strength corrosion-resistant magnesium alloy is higher in strength and better in corrosion resistance, and has wide application prospects in the fields of electronic products and the like.