The invention belongs to the technical field of batteries, and particularly relates to a high-safety lithium ion battery and a preparation method thereof. The battery comprises a shell and a battery cell, the battery cell comprises a positive pole piece, a diaphragm, a negative pole piece and an electrolyte; the positive pole piece contains an inorganic flame-retardant component, the diaphragm is composed of multiple layers, one side, close to the positive pole, of the base material is a coating composed of a polymer with a gel function and a fast ion conductor, and the polymer with the gel function contains a certain flame retardant; the electrolyte contains 0.1 to 0.8 wt% of a fluorine-containing flame retardant with a surfactant function, 0.1 to 3 wt% of a boron-containing additive, 0.1 to 3 wt% of a sulfur-containing additive and 1 to 5 wt% of a pentafluorocyclotriphosphazene additive. The battery has good safety characteristics of preventing overcharge, overdischarge, short circuit and the like, thermal runaway can be effectively inhibited, the safety of the battery is improved, meanwhile, the electrical performance of the battery is not influenced, and the cycle performance of the battery is facilitated.