The invention discloses a power island arrangement structure of a one-on-one multi-shaft gas turbine extraction condensing back-pressure turbine combined cycle power plant. The power island arrangement structure comprises two gas turbines which are linearly arranged outdoors in the open air, wherein two waste heat boilers are arranged in a mirror symmetry manner; a steam turbine is arranged in a steam engine room, and the center line of the steam turbine is parallel to the center line of the gas turbines; the steam engine room is an unequal column space combined factory building; a back-pressure turbine side plant has the column space of 5m, 8m and 5m; a plant intermediate layer and an operating floor have the elevation of 3.9m and 7.9m respectively; an overhauling span is not needed, the back-pressure turbine and extraction condensing turbine are respectively and independently provided with independent access holes of 4.91m*9m and 6.15*9m; two travelling cranes of 32t/5t and 75t/20t are correspondingly configured; lower chord elevation of the plant is 22.73m; a main plant PC and MCC are respectively arranged on a condenser floor and an intermediate layer; a generator outgoing line is arranged on a 3.9m layer; the installation of a main transformer and a standby transformer of a steam turbine set arranged outside the column A can be canceled, and a centralized control building and an electric room are arranged.