In order to meet the requirements of the drive system for the accurate estimation of the speed of traction motor in the fields of speed sensorless control, abnormal diagnosis and prediction of speed sensor, etc. , a real-time speed estimation method based on frequency adaptive phase-locked loop is proposed. Firstly, to solve the problem that traditional phase-locked loop ( PLL) algorithm cannot track the frequency in a large range, a second-order generalized integral phase-locked loop algorithm with feed-forward reference frequency self-adaptive adjustment (RFSOGI-PLL) is proposed to track the fundamental frequency of stator current in a large range in real time. Then, using the relation model of speed of traction motor, fundamental frequency of stator current and cogging harmonic, together with the structural parameters of traction motor, the traction motor speed of the drive system can be estimated in a large range in real time. Finally, the effectiveness of proposed algorithm is verified on a high-power AC drive system. The simulation and field test results show that, compared with the traditional PLL algorithm, the RFSOGI-PLL algorithm proposed in this paper can effectively improve the adaptability of the algorithm to track frequency change, and meet the requirements of traction motor speed estimation in celerity and estimation error.