The invention discloses an AVC control strategy and system of a converter station with a phase modifier. According to the method, coordinative control of the phase modifier and a filter of the converter station is utilized to achieve the AVC control strategy of the converter station, the phase modifier implements a control target issued by AVC through reactive power output, and the control targetcan be busbar voltage of the converter station or the reactive power exchanged by the converter station and an alternating current system; when the converter station senses that the reactive power output by the phase modifier exceeds a setting range and the filter satisfies a free switching condition, the converter station emits a filter switching command to make the phase modifier run within a setting range in a reactive power mode; when the filter of the converter station does not satisfy the free switching condition, the phase modifier achieves the AVC control target as possible as it can,and the converter station no longer cooperates with the filter for switching; during reactive power adjustment of the phase modifier, attention should be paid in real time to ensure that the busbar voltage and output reactive power of the converter station do not exceed the setting range. By adopting the strategy and system, the output reactive power of the phase modifier during steady-state operation can be controlled within a reasonable range.