The invention relates to a method for cooperatively controlling reactive voltage of a wind farm. In the method, a reference voltage value of a busbar is calculated through a logic link according to measured active power, reactive power and a given reference value of reactive power, and the reactive power of each wind turbine is regulated in real-time based on the reference voltage value. The method can cooperatively control reactive output of each wind turbine to enable reactive output of a grid-connection point of a wind farm to meet the variation of system loads so as to restrain the fluctuation of busbar voltage caused by the variation of surrounding loads as well as resist voltage fall of a control point caused by faults of a local electric network, thereby maintaining stable voltage of the wind farm accessing a regional power grid.