Abstarct: It is well known that the reliability of control systems is very important therefore design of fault detection or fault reconstruction methods is very important and vital. In this thesis, first we used sliding mode observers for fault reconstruction and analyzed their performance, then with analyze an adaptive sliding mode observer, we proposed a different adaptive sliding mode observer for fault reconstruction and analyze it’s stability using Lyaponov theorem. For design this proposed adaptive sliding mode observer we do not need the upper bound of fault and it is estimated with adaptation law. In the study, due to uncertainty and disturbance in the system, and their impact on fault reconstruction process, a stable adaptive sliding mode observer for actuator fault reconstruction is proposed, in the proposed method disturbance decoupled is guaranteed. Advantages of the proposed actuator fault reconstruction is fault reconstruction decoupled from disturbance, and need for knowledge about the maximum amplitude of fault is also a eliminated. In addition using sliding mode observers for fault reconstruction we used a dynamic sliding mode control for design a closed loop control system that is robust respect to actuator fault. This proposed method, is a fault tolerant control and if we suppose that the actuator fault is bounded this controller is able to reconstruct it. Moreover in this method, we used adaptation law for estimate the upper bound of uncertainties and disturbances. In this proposed method, sliding surface of dynamic sliding mode control is basis for fault reconstruction and this sliding surface is different. For estimate the unknown states of system, we used a robust LTR observer. Finally, the stability of closed loop system is guaranteed using Lyaponov method