The present invention proposes a control method of the auto-balancing system of an optical disk drive. The present invention adds a procedure of constant rotation speed in the acceleration process of the spindle motor when the rotation speed is below a critical speed. When the rotation speed of the spindle motor is below the critical speed, the position of added mass will be situated at a position at the same side of the unbalance vector of the original optical disk. Thereby the balancing mass will remain at the position of worst balancing effect in the procedure of constant rotation speed. After the procedure of constant rotation speed, the spindle motor will be accelerated to pass the critical speed of the system by the largest torque. Because of inertial effect, when the rotation speed of the spindle motor exceeds the critical speed, the balancing mass will leave from the original position of worst balancing effect and smoothly move to an opposite position of the unbalance vector of the original optical disk. Best balancing effect can thus be achieved.