The invention provides a transient voltage safety control method and system. The method comprises the steps of: when it is detected that faults generate, cutting off a static var compensator device; controlling a rotor-side converter to provide real-time reactive power support to a power grid; when the faults are recovered, re-accessing the cut-off static var compensator into the power grid for operation; and recovering the rotor-side converter to a steady state constant voltage control mode. The transient voltage safety control method and system can inhibit the wind turbine group off-networkrisk caused by the reactive excess in a wind power plant concentrated grid-connected area after the power system suffers from large disturbance.