The invention provides a high-temperature lithium battery electrolyte solution and a preparation method thereof. The electrolyte solution comprises an electrolyte, organic solvents and an additive, the electrolyte is lithium iron phosphate, the organic solvent comprise PC and DEC, and the additive is multilayer graphene; the multilayer graphene accounts for 5-8% of the total mass of the electrolyte solution; and the multilayer graphene comprises multilayer flake graphene and diamond, the diamond is positioned between two adjacent layers of the multilayer flake graphene, and the diamond corresponds to carbon atoms of the multilayer flake graphene one to one. The new additive material added to the electrolyte solution of a lithium battery enhances the heat conduction and electricity conduction performances of the battery, so the battery can uniformly transfer heat in a high temperature environment during working in order to make the internal temperature of the battery be reduced and tends to stability; and the good electricity conduction performance can effectively reduce the internal resistance of the battery to make the temperature rising of the battery during working reduced, makes the battery adapt to a high temperature reaching up to 75 DEG C, improves the use safety of the lithium battery, and prolongs the service life.