The present invention discloses a Lithium ion battery and an electrolyte thereof, the electrolyte comprising an organic solvent, a lithium salt and an additive. The additive comprises a cyclic fluoro carbonate (A), a cyclic phosphazene (B), a cyclic sulfate and a lithium fluoro oxalate borate (D). The lithium fluoro oxalate borate (D) has following formula: Compared with the prior art, the electrolyte of the present invention may form a stable CEI and SEI film on the surface of positive and negative electrodes, protect the interface between positive and negative electrodes, improve the acidic atmosphere of Lithium ion battery electrolyte, and reduce the damage effect of HF on the interface between positive and negative electrodes, while reducing low temperature resistance of lithium-ion battery, improving cycle life, high temperature storage performance, safety performance and rate capability of lithium-ion battery.