The invention discloses a ballasting method in large-span girder cantilever construction. The ballasting method comprises the following steps of: A10, constructing an enlarged foundation of temporary piers for a side span girder, and arranging an embedded steel strand; A20, constructing the temporary piers on the enlarge foundation; A30, detaching the temporary piers after the side span girder is erected; A40, mounting distributive girders on a bridge deck of the side span girder, and making a steel strand pass through drain holes on the bridge deck of the side span girder and fixedly connected with the embedded steel strand; A50, when the factor of safety against overturning of the girder cantilever is less than 1.3, beginning ballasting, tensioning the steel strand by using a tensioning jack arranged on the bridge deck of the side span girder, lifting the enlarged foundation, and anchoring the upper end of the steel strand to the distributive girders to ballast the side span girder; and A60, after a girder is folded, descending the enlarged foundation by using the tensioning jack and the steel strand to unload the ballast. By the method, the enlarged foundation is integrated with a ballasting material, and the method has the advantages of saving materials, not occupying girder operating space, not influencing the jacking and drop and longitudinal shift of the girder, and the like.