Abstract: Due to the transmission capacity of ultra high-voltage direct current（UHVDC） increasing, intensive HVDC inverter stations located and load high-density accessing, voltage stability has become one of the important factors of threating to the security and restricting the ability to accept loads for the receiving end power grid. In this paper, the relationship between reactive power and active power was analyzed based on the quasi-steady-state analytical equations of inverter firstly. Time domain simulations show the dynamic difference between inverter consumption and capacitor bank exportation of the capacitive reactive power, so the inverter station can be as dynamic reactive power source to improve the voltage stability of the receiving end power grid by HVDC power backing down. The start criterion and the revocation criterion of HVDC emergency power control were put forward, and based on the disturbed trajectory of commutation bus voltage at inverter station, the control strategy with online application prospects was also proposed. Large disturbance time-domain simulation results got from the receiving end power grid of Humeng-Yuxi ?800 k V/8 000 MW UHVDC transmission system verified the recommended control strategy is a cost-effective measure to enhance the voltage stability level and to circumvent load shedding.