The invention discloses a lithium ion battery activation method, which comprises the following steps that: 1, in a constant current charging stage, a current range is 0.02 to 0.1 CA, and the charging time is 1.5 to 3 hours; 2, in a constant current and constant voltage charging stage, the constant current range is 0.1 to 0.3 CA, the constant current charging is stopped until a preset voltage is reached, and the subsequent constant voltage charging is stopped until the current is 0.01 to 0.05CA; 3, in a constant current discharging stage, a current range is 0.05 to 0.2 CA, and the discharging time is 1 to 4 hours; 4, in a constant current and constant voltage charging stage, the constant current is 0.05 to 0.2 CA, the constant current charging is stopped until the preset voltage is reached, and the subsequent constant voltage charging is stopped until the current is 0.01 to 0.05CA; 5, in the constant current discharging stage, the current range is 0.05 to 0.2 CA, and the discharging time is 1 to 4 hours; and 6, in the constant current and constant voltage charging stage, the constant current is 0.05 to 0.2CA, the constant current charging is stopped until the preset voltage is reached, and the subsequent constant voltage charging is stopped until the current is 0.01 to 0.05CA. By the lithium ion battery activation method, a phenomenon that lithium ions are separated after a lithium battery is activated can be avoided.