The invention provides a large phase modifier start grid-connected control method, belongs to the technical field of motor controls. The method targets the problems that the large phase modifier when started is dragged by a SFC to a 105% rated speed then gets into the running down state, and boosted grid causes frequency difference and phase angle difference uncontrollable issues, and proposes a control strategy for controlling the SFC removal angle and excitation system at reclosing time, to maximally reduce phase modifier grid-connected impact on the device body and the system. The method can effectively solve the problem that under the condition of unit turning down, the switch of phase modifier start excitation and the self-shunt excitation exciting mode cause grid connecting process to be uncontrollable, the controllability of poor frequency and poor phase angle at grid connection is improved while success rate is ensured, and the impact problem caused by phase modifier grid connection is greatly reduced, the security stability and grid success rate of large phase modifier are improved, the method has significances on the security, efficiency and reliability of running large phase modifier.