A state space force identification method was presented to accurately solve the inverse problem of dynamic force identification by measuring the structural responses. This method is based on precise computation for force identification model and regularization technique. A singular valued decomposition (SVD) method was introduced to analyze the essential illposedness of inverse problem of force identification, and the Tikhonov regularization technique was used to solve this illposed problem in order to obtain a stable solution. Finally, the proposed method was successfully applied to reconstruct the time history of forces acting on a plane frame structure, and the results show that this method is a promising way to reconstruct the time history of exerting force on structure.