Abstract: In order to expand commercial utilization area, a floor with the area of 2 060 m2 is pos-t built in the ground floor which is 61 2 m high. The design thought is presented, that is: pos-t building corbel from the reinforced concrete column, making the corbel supporting post-built double beams, and making the double beams as main beam and supporting cross secondary beam and floor. The design process and the relative joint constructions of pos-t built corbel and pos-t built double beams are introduced, which can be served as reference for the the design of pos-t built floor of similar projects.