Abstract: The concrete for frame columns on the 5th floor for a tall building is unacceptable.Therefore,the method of replaced concrete is selected.Computer-control system and strain gauges are used during construction by this strengthening method;meanwhile mechanical jacks are also used in unloading process,by which the internal forces,deformation,residual deformation of the structure at replaced concrete position can be reflected accurately.The displacement of the structure is monitored by micrometers,which provides reliable basis for unloading,thus the safety of the operators and the structure can be ensured during the construction of strengthening the structure.