The invention belongs to the technical field of metal materials, and relates to a preparation method of high-strength magnesium-tin-zinc-lithium-sodium alloy. The alloy comprises the following components by weight percent: 3 to 9 percent of Sn, 1 to 2 percent of Zn, 0.5 to 1.5 percent of Li, 0.5 to 1.5 percent of Na, and the balance of Mg and impurity elements Si, Fe, Cu and Ni, and the total amount of the impurity elements is less than 0.02 percent. The preparation method comprises the following steps: (1) preparing materials; (2) smelting; and (3) performing the heat treatment. The high-strength magnesium-tin-zinc-lithium-sodium alloy has the beneficial effects that the Zn element is added into the magnesium-tin alloy, so that the precipitation of a reinforcing phase can be promoted in an aging process, and the peak-value aging hardness can be improved; and by adding the elements Li and Na, by utilizing the synergistic effect of the two elements lithium and sodium, the aging hardening process can be accelerated, the performance of the high-strength magnesium-tin-zinc-lithium-sodium alloy can be improved, and the density of the alloy can be reduced.