The invention discloses a construction method for an assembled building cantilevered element, and belongs to the technical field of the assembled building. The construction method for the assembled building cantilevered element comprises the steps that the construction is prepared; the element is hoisted; a pendant-fitting is hanged, and the pendant-fitting is connected with the element; the elevation, verticality and levelness of the element is adjusted; a reserved steel bar of the element is fixed with a plate tendon; slab concrete is poured; and after the concrete reaches the design strength, the pendant-fitting is removed. The construction method for the assembled building cantilevered element is based on the steel mixing assembled structure system, without the need for using a traditional support system, the construction site is clean, neat, and unblocked, the construction period is short and the construction cost is low.