The invention, which belongs to the technical field of online dynamic balance of the rotor, discloses a fast and high-precision balancing method for an online dynamic balance system of a polar coordinate type grinding wheel. According to the online dynamic balance method, defects of the stepwise optimization method are overcome. To be specific, the proper initial included angle of the two balanceplates can be quickly searched, so that the balance efficiency is improved; because balance operation criterion vibration values are classified into vibration effective values and vibration power frequency components based on balance stages, the coordinated optimization of the balance speed and balance accuracy is realized; the step size is adjusted to be variable step sizes to adapt to unbalanceswith different sizes, thereby considering the balance speed and accuracy simultaneously; and the adverse effects caused by the inconsistent rotation steps of the two balance plates, so that the balance balance speed and accuracy are greatly improved. Especially, when the unbalance amount is within a specific zone, the balance speed is increased and the effect becomes obvious.