The invention relates to a method for manufacturing a whole section of a closure section of a steel truss beam of a highway and railway dual-purpose bridge. The method comprises the following steps that 1) closure section plate units and rod pieces are manufactured, particularly, the plates and rod pieces with the required size are cut out according to a design drawing, and two cuts are reserved on the closure opening side; 2) bridge deck slabs and trusses are assembled and spliced at the closure section, particularly, the rod pieces are assembled and spliced into a main truss and an auxiliarytruss bridge face, then, multiple sections are continuously matched and spliced, and the slabs are spliced according to the design drawing; 3) anticorrosive coating is carried out on the bridge deckslabs and the trusses; and 4) the whole section of the closure section is spliced, particularly, a scheme that the closure section and steel truss beams connected to the two sides of the closure section are not less than three continuous whole sections is adopted, splicing is carried out from the non-closure opening to the closure opening side direction, wherein a single section assembly process comprises splicing of a railway ridge deck slab, splicing of main trusses on two sides, splicing of a middle roadway bridge deck slab, splicing of an auxiliary truss inclined strut and splicing of auxiliary trusses on two sides and a side roadway bridge face. The method has the advantages of being high in manufacturing precision, high in construction efficiency and low in safety risk.