The embodiment of the invention provides a power system voltage stability control method and device, and the method comprises the steps: building a power system model with a virtual synchronous generator, and obtaining an equation set of a system; analyzing an equation set of the system by utilizing a bifurcation theory to obtain a maximum value of reactive power of the load; and controlling the system load according to the maximum value of the reactive power of the load. According to the invention, the maximum value of the reactive power of the load is determined by performing bifurcation analysis on the constructed power system model with the virtual synchronous generator, the load is limited through the maximum value of the reactive power, and the load power is prevented from exceedingthe maximum value, so that a basis is provided for determining the wind power transmission limit and improving the voltage stability of the power system.