The invention discloses a medium-strength high-toughness aluminum lithium alloy and a preparation method thereof. The aluminum lithium alloy comprises the following components in percentage by weight: 2.2 to 3.2 percent of Cu, 1.1 to 2.0 percent of Li, 0.10 to 0.70 percent of Mn, 0.05 to 1.0 percent of Zn, 0.05 to 0.16 percent of Zr, 0.10 to 0.80 percent of Mg, 0.2 to 0.6 percent of Ag, less than or equal to 0.10 percent of Si, less than or equal to 0.10 percent of Fe, less than or equal to 0.12 percent of Ti, less than or equal to 0.15 percent of other impurities (less than or equal to 0.05 percent of single impurity), and the balance of Al, wherein 1 to 5 alloy elements of Mn, Zn, Mg, Ag and Zr can be selectively added. The preparation method comprises the following steps of: melting the raw material, performing furnace refining, standing, and casting into alloy ingots with the needed specification. The alloy ingots are preferably homogenized, can be processed and molded through hotextrusion, hot rolling or hot extrusion, and can be used for processing parts after heat treatment of preferable technology. The novel medium-strength high-toughness aluminum lithium alloy material has the advantages of uniform microscopic structure, stable performance, suitability for manufacturing thick plates and extruded sections, the ultimate tensile strength of over 440MPa, the elongation rate of over 6 percent and the KIc of over 36MPam1/2.