The invention discloses a method and system for measuring a reactive current compensation rate based on a voltage step method. The method comprises the steps that a reactive current compensation function is introduced into a generator which operates stably, a given value of the generator terminal voltage is modified according to a preset step proportion, and voltage step is achieved in the generator terminal; generator terminal voltage given values, generator terminal voltages and generator reactive power before and after voltage step of the generator terminal are recorded; generator stator voltages and reactive power of two steady-state points before and after voltage step of the generator terminal as well as generator reactive currents under the two steady-state points are selected; reactive current compensation reactance is calculated according to the generator terminal voltage given values, the generator terminal voltages, the generator reactive currents and the generator terminalvoltages before and after voltage step of the generator terminal; and the actually measured reactive current compensation rate is calculated according to the reactive current compensation reactance and the per-unit base value of the generator reactance.