The invention discloses a bi-directional adjustable post-installed anchor device used for erecting steel cantilever beams. The device comprises a steel girder extension section, wherein the upper and lower parts of the steel girder extension section are provided with an upper carrying pole beam and a lower carrying pole beam, an inhaul cable is connected with the upper carrying pole beam and the lower carrying pole beam, the upper carrying pole beam or the lower carrying pole beam does not contact with the steel girder extension section, one end of the inhaul cable is connected with a height adjustment device; and the lower carrying pole beam is connected with a steel strand. The device of the invention provides larger anchored force while not fixing the steel girder so that the steel girder can be moved within a large range along the longitudinal direction of a bridge, the steel girder along the vertical direction of the bridge can be adjusted finely, and the steel girder erection and successful closure of the bridge can be ensured through bi-directional movement. The large-tonnage roof beam-dropping device which is must used in conventional closure of the bridge can be avoided so that the device of the invention can be used to simplify the construction process and ensure simple structures.