The invention discloses a safe stress conversion construction method for the improvement on a main structure of a subway station. The safe stress conversion construction method comprises the following steps: the first step is construction of a novel underground diaphragm wall; the second step is broadening construction, wherein a top plate, a middle plate and a bottom plate are respectively broadened from top to bottom, the top plate, the middle plate and the bottom plate all need broadening, and the broadening construction method of the top plate, the broadening construction method of the middle plate and the broadening construction method of the bottom plate are the same; an actual broadening construction process comprises broadening segment division, first-stage broadening segment broadening and second-stage broadening segment broadening; the third step is construction of a novel side wall, wherein a second left side wall and a second right side wall are constructed on the left side and the right side of the multiple broadened plates respectively after broadening construction in the second step is completed. According to the safe stress conversion construction method for the improvement on the main structure of the subway station, the steps are simple, the design is reasonable, implementation is convenient, investment cost is low, construction progress is fast, the construction effect is good, and the improvement process of the main structure of the subway station can be completed simply, conveniently and quickly.