The invention discloses an electrolyte for a lithium-ion power battery, which comprises lithium salts, organic solvents and additives, wherein the lithium salts comprise at least one of LiODFB, LiPF6, LiClO4, LiBF4, LiAsF6, LiCF3SO3, LiN(SO2CF3)2 and LiBOB; the invention also discloses a preparation of the electrolyte, which comprises the following steps: mixing the organic solvents after impurities and water are removed; (2) adding the lithium salts in the mixed organic solvents, evenly stirring till the solution is clear and has no sediments, and allowing the solution to stand for at least half an hour to obtain mixed solution; (3) adding the additives into the mixed solution, evenly stirring, and then allowing the mixed solution to stand to obtain the required electrolyte. The invention improves the cycle performance of the battery at the high temperature, prevents gas explosion caused by electrolyte decomposition, can remarkably promote the long-life function of the volume conservation rate of the lithium-ion power battery at the high temperature, and has simple preparation method and easy industrialization production simultaneously.