Induction motor is widely used in various machine tools. The variation of its rotor time constant can reduce the rotor flux orientation accuracy, and further reduce the torque control precision. Taking the induction motor that used in a certain machine tool as the research object, the effects of the rotor time constant variation on the rotor flux orientation control of induction motor were analyzed in details, including the effects on the rotor flux and the stator voltage. Based this analysis results, a daxis voltage based rotor time constant identification method for induction motor was proposed. The simulation and experimental system were established, and simulation and experimental studies were carried out. The simulation and experimental results show that the proposed rotor time constant identification method not only can be used to realize rotor time constant online identification, but also has good dynamic response speed and antidisturbance performance. Moreover, it can provide better power input for machine tools and same application areas.