The invention provides an optimization method and system for over-excitation of an excitation regulator. The over-excitation limit optimization method of the excitation regulator comprises the following steps: determining an inertia time constant; collecting an excitation current of a generator, and calculating a first calculation result according to an inertia time constant and the excitation current; comparing the first calculation result and the first comparison value to obtain a first comparison result, and determining an output result according to the first comparison result; when the output is a second value, initiating an over-excitation limit inverse timing adjustment to reduce the excitation current to a first preset value. Different inverse time limit can be adjusted according todifferent initial excitation currents before a fault, that is, the unit can have higher strong excitation ability at low load operation and lower strong excitation ability at high load operation, soas to ensure that the power grid can provide adequate and appropriate reactive power support during multiple cascading faults and maintain the safe operation of the power grid.