The invention discloses a construction method for a prefabricated box girder support in a complex city environment, and belongs to the technical field of bridge engineering, and the construction method comprises the following steps: S1, carrying out surveying and setting out; S2, laying tracks, and assembling a bridge girder erection machine; S3, enabling the bridge girder erection machine to erect the box girder in a high-low mode; S4, mounting a support; S5, fixing the box girder; S6, carrying out bridge deck girder feeding and box girder erection of the bridge girder erection machine; and S7, performing crossing of the bridge girder erection machine. The truss double-beam bridge girder erection machine is adopted, a main truss of the bridge girder erection machine adopts standing rod pieces, transportation is convenient, the assembling and disassembling speed is high, the cost is saved, the machining period is shortened, high-low hoisting construction is adopted, a girder lifting station is not arranged, box girders are transported to the erection position through an offline transport vehicle, and the bridge girder erection machine directly lifts and erects the girders; a girder is lifted in the middle of an erection pier position, the mode that the front portion is high and the rear portion is low is adopted, box girders are lifted and longitudinally moved through a crane carriage, 1-2 spans are installed through a crane before a bridge girder erection machine is installed, and installation of the bridge girder erection machine is facilitated.