The invention provides a metal lithium alloy as well as a preparation method and application thereof. The preparation method comprises the following steps of (1) extracting a purified alkali metal-containing aqueous phase with a composite extraction organic phase, and separating liquid to obtain an alkali metal-rich salt organic phase; (2) washing the alkali metal-rich salt organic phase obtainedin the step (1) with a washing liquid; and (3) electrolyzing the washed alkali metal-rich salt organic phase to obtain the metal lithium alloy. According to the method, the lithium alloy is extractedfrom lithium resources, the lithium alloy can be directly used as a lithium negative electrode, comprehensive utilization of the resources and short process preparation of the material are achieved, energy consumption steps such as reverse extraction crystallization transformation and the like are not needed, the technical advantages are obvious, and the energy-saving effect is remarkable; and thealloy lithium negative electrode is applied to a lithium battery, the activity of the lithium negative electrode can be reduced, and the side reaction between the electrode and the electrolyte is reduced. It is guaranteed that the negative electrode surface charge distribution of the lithium battery is uniform, the electric field is stable, uniform deposition of metal lithium is realized, the growth of lithium dendrites is relieved, and the stability and the safety of the metal lithium battery are improved.