The present invention discloses a UPFC (unified power flow controller) series-parallel converter coordinated control strategy capable of improving the voltage supporting strength of an alternating-current bus-bar. According to the UPFC series-parallel converter coordinated control strategy, the amplitude of the voltage of a controlled alternating-current bus-bar during the operation of a power grid is monitored; when the voltage of the alternating-current bus-bar exceeds a limit, characteristic signals which can reflect the limit-exceeding degree of the voltage of the alternating-current bus-bar are calculated; an UPFC series converter reactive power flow command value and a UPFC parallel inverter reactive power command value are automatically adjusted through an alternating-current bus-bar voltage coordinated control algorithm; and UPFC system-level adjustment capacity is utilized to the greatest extent, so that the alternating-current voltage can be controlled to be in a safe and stable operation range. Thus, with the UPFC (unified power flow controller) series-parallel converter coordinated control strategy adopted, an effective means can be provided for solving the voltage supporting problem of the power grid after an ultra-high-voltage system is connected into a system and improving the dynamic/static voltage supporting capability of the system to the greatest extent.