Abstarct: One of the main challenges in a wind turbine system is to improve its reliability in order to prevent irreparable damage and to reduce system performance due to faults; Therefore, providing a reliable and fault tolerant control structure for the wind turbine system is essential. In this thesis, in order to ensure the optimal condition of the system in the presence of faults, the design of a fault tolerant control of the pitch system is considered. First, the fault detection and diagnosis system for the wind turbine system is examined. In this regard, using the linear matrix inequlity technique, the fault tolerant control system of the sensor and actuator is designed baxsed on the TSK model. The proposed method has the ability to estimate the fault and behavior of state variables. Then, for the nonlinear model of wind turbine, the guarantee of system performance in the presence of actuator fault is achieved by designing a fuzzy observer. The fuzzy system is used to approximate unknown terms. Next, in order to strengthen the performance of the system, a robust fuzzy observer is designed using the term disturbance descxriptor. The design mechanism is baxsed on the backstepping method and the guaranteed behavior of the wind turbine system will be tangible in the presence of a pitch angle sensor fault. In all the proposed methods, the stability of the closed-loop system is proved by Lyapunov theory. The simulation results show the efficiency of the proposed controllers in achieving the control objectives for the wind turbine system.