The invention provides an automatic voltage control method and system of a wind power plant. The automatic voltage control method comprises the steps of receiving a power grid voltage instruction set value, and monitoring the power grid voltage in real time; when the power grid voltage fluctuates, controlling SVC/SVG equipment to output reactive power to perform reactive compensation; and monitoring the value of the reactive power output by the SVC/SVG equipment in real time, and if the value of the reactive power output by the SVC/SVG equipment is greater than the set value, distributing the part, which exceeds the set value, of the reactive power output by the SVC/SVG equipment to a wind generator group, wherein the wind generator group outputs reactive power to perform reactive compensation. The wing generator group is high in reactive capacity, high in number of equipment, high in communication data size, long in reaction time and low in reactive adjustment speed, so that the SVC/SVG equipment is controlled to output reactive power firstly, and the SVC/SVG equipment and the wind generator group perform coordinative operation, so that the reaction time of an AVC controller is greatly reduced, voltage adjustment is more stable, and requirement of quick adjustment of the reactive power of the power system can be satisfied.