The invention relates to a method for detecting the control capacity of a regional dispatching side in the provincial-regional coordinated voltage control, and belongs to the technical field of power system automatic voltage control. In the method, indexes QNI, QND, QNIst and QNDst for describing reactive control capacity of the regional dispatching side are designed, wherein the QNI refers to reactive capacity capable of being increased by the current regional dispatching radiation power grid; the QND refers to reactive capacity capable of being decreased by the current regional dispatching radiation power grid; the QNIst refers to reactive capacity capable of being increased in a transformer substation where the current regional dispatching gate is positioned; and the QNDst refers to reactive capacity capable of being decreased in a transformer substation where the current regional dispatching gate is positioned. On the basis that whether the weighting coefficient of reactive power equipment i1 is 0, online calculation of the indexes of the reactive voltage control capacity of the regional dispatching side is realized. The method can timely provide basis for calculating a provincial-regional coordinated voltage control strategy so as to ensure normal operation of the provincial-regional coordinated voltage control.