The invention provides a formation method for a lithium ion battery. The formation method comprises the following steps of adopting different low currents, performing constant-current charging on a to-be-formed lithium ion battery at different stages to obtain a pre-formed lithium ion battery, and standing; adopting first current, performing constant-current charging until a charging cut-off voltage of the lithium ion battery is achieved, then performing constant-voltage charging for the first time, and standing for the second time; adopting second current, performing constant-current discharging until a discharging cut-off voltage of the lithium ion battery is achieved, and standing for the third time; repeatedly executing the above steps; and finally, adopting a third current, performing constant-current charging to a fourth voltage, and performing constant-voltage charging again. In the formation process of the lithium ion battery, namely the first round of the charging process, pre-formation and main formation steps are performed; and low-voltage trickle formation at different stages is adopted in the SEI membrane forming stage in the front stage, so that co-embedding of solvent Li ions can be effectively prevented, growth time of membrane compact components is increased, the composition and structure are stabilized, and a more compact SEI membrane is formed on the surface of a negative electrode material.