The invention discloses a lower-limit-voltage-changing reactive power control system and method of a voltage source converter. The lower-limit-voltage-changing reactive power control method of a voltage source converter includes the following steps: performing control of lower limit voltage changing on the alternating current side of the voltage source converter to obtain a first output current value, performing reactive power control on the alternating current side of the voltage source converter to obtain a second output current value, and performing upper limit voltage control on the alternating current side of the voltage source converter to obtain a third output current value; and selecting the smaller current value among the second output current value and the third output current value as the first reference current value, comparing the first reference current value with the first output current value, selecting the greater current value among the first reference current value and the first output current value as the reactive current reference value of the voltage source converter. The lower-limit-voltage-changing reactive power control system and method of a voltage sourceconverter can effectively suppress the fluctuation of the alternating voltage and improve the operational stability of the alternating current grid connected to the voltage source converter.