A 1 GPa high-strength high-modulus aluminum-based light medium-entropy alloy and a preparation method thereof. An atomic expression of the designed medium-entropy alloy is AlxLiyMgzZnuCuv, subscripts representing the molar percentage of each corresponding alloy element, where x+y+z+u+v=100, x is 79.5-80.5, y is 1.5-2.5, z is 1.5-2.5, u is 13.5-14.5, and v is 1.5-2.5. The phase structure of the involved alloy is mainly based on a face-centered cubic (FCC) solid solution. The present invention obtains high performance aluminum alloy ingots through vacuum induction smelting and direct casting, and features low energy consumption, decreased cost, and simple operation in the preparation process, which cater to the high requirements on cost, strength and plasticity of light alloys applied in the high-end manufacturing industries such as aerospace and automobile electronics nowadays.