The rotor speed measurement of doubly fed induction generator (DFIG) is very important to its control system design, but many problems may arise when applying traditional speed sensor. So, it is necessary to study the speed-sensorless measuring technique. Firstly, a novel speed measuring method based on soft-sensor theory is proposed in this paper. Secondly, the mathematical model of DFIG is given, and the soft-measuring method of dq-axis rotor current components that can't be directly measured are discussed. Thirdly, a soft-sensor of DFIG based on stator voltage oriented control strategy is constructed. Then, the speed observer and the speed-sensorless vector control strategy based on the soft-sensor are proposed. Finally, the simulation is performed on the MATLAB/Sim Power Systems, and the results demonstrate the validity of the proposed method.