The invention discloses an electrolyte for a lithium ion battery. The electrolyte comprises an organic solvent, electrolyte lithium salt, and a combined additive containing gamma-butyrolactone, ethylene sulfate, adiponitrile and fluoroethylene carbonate, wherein the electrolyte comprises the following components based on weight percentage: 0.1-40% of gamma-butyrolactone, 0.1-5% of ethylene sulfate, 0.1-10% of adiponitrile and 1-10% of fluoroethylene carbonate. According to the electrolyte, the combined additive is added to the lithium ion battery electrolyte, so that the safety performance, the high-temperature storage performance and the cycling performance of the lithium ion battery in a high-voltage system can be obviously improved. In addition, the invention also discloses the lithium ion battery.