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 additive (A) cyclic fluoro carbonate, additive (B) cyclic phosphazene (B), and additive (C) cyclic sulfate. The additive B cyclic phosphazene has the following general structural 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, thereby improving cycle life, high temperature storage performance, and safety performance of lithium-ion battery.