The invention provides a method for determining the control range of operation voltage of a 500kV bus of an extra-high voltage alternating-current transformer substation. The method comprises the following steps: determining an upper limit and a lower limit of the operation voltage of the 500kV bus which is determined by the operation voltage of a 500kV device; determining an upper limit and a lower limit of the operation voltage of the 500kV bus which is determined by voltage withstand level of an extra-high voltage device; determining an upper limit of fluctuation of the operation voltage of the 500kV bus which is caused by an opening/closing loop of an extra-high voltage line; determining an upper limit and a lower limit of fluctuation of the operation voltage of the 500kV bus which is caused by power fluctuation of the extra-high voltage line; determining an upper limit and a lower limit of fluctuation of the operation voltage of the 500kV bus which is restricted by a special device; determining the control range of the operation voltage of the 500kV bus of an extra-high voltage alternating-current transformer substation. The method for determining the control range of the operation voltage of the 500kV bus of the extra-high voltage alternating-current transformer substation is capable of providing a strong support for arranging an operation manner of an interconnected electric power system and determining voltage controlling measures and has the advantages of strong adaptability and comprehensive consideration factors.