The invention discloses a lithium ion battery formation method. A negative electrode active substance of a lithium ion battery comprises a lithium-rich manganese-based positive electrode material. Theformation method includes at least three times of charge-discharge cycles; in the two former charge-discharge cycles, charge cut-off voltage is lower than 4.4V, discharge current is higher than charge current, and the second-time charge current is higher than the first-time charge current; in the last charge-discharge cycle, the charge cut-off voltage is not lower than 4.4V, and the charge current is not lower than the second-time charge current. By the step voltage charge-discharge formation method, a stable SEI film can be formed on the surface of a negative electrode in repeated low-voltage charge-discharge processes while a stable CEI film is formed on the surface of a positive electrode, side reaction between electrolyte and an electrode piece can be inhibited, gas generation is reduced, and accordingly the problem of battery swelling is solved. In addition, by the method, structural stability and capacity exertion of the lithium-rich manganese-based positive electrode material under a high voltage can be improved, and the cycle performance and the energy density of the battery are improved as well.