In view of the unclear physical meaning of the torque angle(or power angle)of cage rotor brushless doubly-fed motors in steady state operation,the electromagnetic torque of the motors in steady state was derived from analyzing the internal magnetic field of the motors,and the analytical expression for the torque angle calculation was obtained.On this basis,the physical meaning of the torque angle of the motors was revealed.By finite element simulation,the theoretical derivation was validated.The research results not only help to simplify the steady-state simulation process of cage rotor brushless doubly-fed machines,but also provide a theoretical basis for a deeper understanding of the internal energy conversion mechanism of cage rotor brushless doubly-fed machines in steady state operation.