The invention discloses a truss-box equivalent design method of a combined truss-web member girder bridge. By means of the method, the combined truss-web member girder bridge is transformed into a concrete box girder bridge through an equivalent method, so that the design of the combined truss-web member girder bridge is transformed into the design of the concrete box girder bridge. According to the truss-box equivalent design method of the combined truss-web member girder bridge, the original shape of the combined truss-web member girder bridge can be maintained to the utmost, and the most essential mechanical characteristics of the combined truss-web member girder bridge are embodied. According to the truss-box equivalent design method of the combined truss-web member girder bridge, a structure composed of two materials is equivalent to a structure composed of the same material; when the overall design is conducted, it is unnecessary to consider a connecting method among different materials, designing is convenient, and designing efficiency can be greatly improved; the discrete struct of the combined truss-web member girder bridge is transformed into the continuous struct of the concrete box girder bridge, so that the structure is simplified, and the method brings convenience to analysis and design.