The invention discloses a method for improving stress performance of a negative bending moment zone ofa steel-concrete combined multi-box continuous beam bridge. The continuous girder bridge built by using the method comprises multiple horizontally connected separate small box beams. The upper portion of each small box beam is a concrete bridge surface plate. The lower portion is a steel box beam. The concrete bridge surface plate and the steel box beam are connected into an integral body by the shear force of the top flange of the steel box beam. Normal stress steel bars and constructional steel bars are arranged in the concrete bridge surface plates of the whole bridge. Normal horizontal and longitudinal stiffening ribs are arranged in the steel box beams. The longitudinal stress steel bars in the concrete bridge surface plates of the negative bending moment zone are intensified in density. After the steel box beams is erected, the surface plates are grouted and the preformed holes are prepared, concrete is grouted in the steel beam base plates of the negative bending moment zone through the holes, the concrete grade is identical to the concrete grade of the bridge surface plates. The method can increase the compression strength of the steel box beam base plate, improve the unfavorable stress condition that the steel box beam base plates in the negative bending moment zone is bent by pressure.