Abstract: The present invention relates to a high-strength and high-toughness high-magnesium aluminum alloy and a preparation method thereof. The high-strength and high-toughness high-magnesium aluminum alloy provided by the present invention comprises the following components in percentage by mass: 5.54-6.80% of Mg, 0.50-0.60% of Mn, 0.12-0.16% of Zr, 0.30-0.36% of Er, less than or equal to 0.3% of Si, less than or equal to 0.2% of Fe and the balance of Al. In the present invention, the content of each element is strictly controlled, after a proper amount of Zr and Er rare earth elements in mass percent are added into the aluminum alloy, the mass percent of Mg element in the aluminum alloy is further controlled, so that the Mg element can interact with the rare earth elements efficiently, and the strength and toughness matching of the aluminum alloy with an Al—Mg—Mn—Zr—Er multi-element system can be improved.