The invention relates to a method for widening a steel-concrete combination, which is a technological method for widening an original concrete bridge. The method widens the original concrete bridge by adopting an integrally and jointly stressed steel-concrete composite beam comprising a concrete bridge deck and a steel beam. The method comprises the following steps: firstly roughening and reinforcing bar loading treatments are carried out on the main beam of the original bridge, a steel plate-concrete composite anchoring and connecting piece is arranged to connect the main beam with the transverse connecting steel beam of the original bridge; the main beam of the original bridge is connected with the steel-concrete composite beam into a whole body through the transverse connecting steel beam; roughening and transverse connecting reinforcing bar loading are carried out on the bridge deck of the original bridge, the bridge deck of the original bridge is extended to the upper bridge deckarea of a widened beam, and the widened bridge deck is concreted to form a whole body. Compared with a traditional widening method, the method has the advantages that the structural height can be reduced, the structural dead weight can be reduced, and the lower structural cost can be reduced. Meanwhile, the composite beam is convenient to be produced, the installation quality is high, the construction is economic, convenient and fast, the influence to the normal traffic of the current bridge is small, and the deficiency of the method for widening the traditional concrete beam is overcome.