Precise positioning device and positioning method for center of cableway pipe of cable-stayed bridge

The invention relates to a precise positioning device and method for the center of a cableway pipe of a cable-stayed bridge and relates to the technical field of bridge construction, the positioning device comprises a base, a measuring rod and a plurality of positioning pieces, and the positioning device has a first use state and a second use state; when the measuring rod is in the first use state, one ends, far away from the base, of all the positioning pieces abut against the circular contour line of the inlet of the cableway pipe, the measuring rod is in a vertical state, and the prism is arranged on the measuring rod, so that the prism and the center of the inlet are located on the same plumb line; in the second use state, two of all the positioning pieces abut against the oval contour line of the outlet of the cableway pipe, at least one of the remaining positioning pieces abuts against the inner wall of the cableway pipe, the ends, away from the base, of all the positioning pieces are located on a circl