From the basic principle of rotating machines stable operation， a rotor speed redundant signal observation method for doubly-fed induction generator（DFIG） is proposed， and the fault tolerant control strategy of the rotor speed sensor is studied by the fault diagnosis. First， by introducing the role of rotor speed signal on the wind turbine driven DFIG control system， a rotor speed observer model of DFIG based on a PLL method is established. Secondly， by the simulation on the operation performance for wind turbine driven DFIG under a step change of wind speed， the output values of the proposed rotor speed observer are compared with the results from the rotor speed sensor output and the closed-loop speed observer from the presented literature respectively. Finally， an adaptive threshold speed signal fault diagnosis method and fault-tolerant control strategy is also proposed， using the examples of the possible soft and hard fault types of the rotor speed sensor， the fault-tolerant control performance of wind turbine driven DFIG is investigated. The compared results show that the proposed speed observer model has a better performance to achieve the redundancy for the rotor speed signal， and the fault-tolerant control of the rotor speed sensor can also be exactly performed when the sensor has a fault.