The authors have been proposed the steel-concrete double composite twin I-girder bridge. However, the composite action and the design method by adopting the headed studs welded both on the lower flange plate and web plate at lower concrete slab in double composite twin-I girder bridges is not yet clarified perfectly. Based on the results of the static push-out test for headed studs, therefore, this paper presents a design method of the stud, which are arranged both in horizontal and vertical directions.