In this paper, the estimation method of reaction force for electro-hydraulic servo system for movement is discussed. This reaction force estimation method is based on sliding perturbation observer that is robust observer technique. Before estimating reaction force, the modeling of electro-hydraulic servo system is processed. Before the fine modeling parameters of electro-hydraulic servo system, modeling equation is obtained through cylinder equation using expansion and shrinkage stroke process. After finding modeling equation, the obtaining accurate modeling parameter is carried out from signal compression method. After defining modeling parameter, reaction force estimation is operated by sliding perturbation observer. The analysis result of estimation for reaction force will be used for bilateral control with master-slave structure.