The invention discloses a rail transit traction system and a control method and device of a permanent-magnet synchronous motor thereof. The method comprises: a rotating speed of a motor is obtained and the rotating speed of the motor is determined; when the rotating speed is lower than a first preset rotating speed, the motor is controlled by using an asynchronous SVPWM way and a synchronous SVPWM way, so that the motor cam work at a constant torque; when the rotating speed is larger than the first preset rotating speed and is smaller than a second preset rotating speed, a modulation degree of the motor is obtained and the motor is controlled by using an SHEPWM way based on the rotating speed and the modulation degree, so that the motor can adapt to pulse modulation at different rotating speeds and under different torques; and when the rotating speed is larger than or equal to the second preset rotating speed, the motor is controlled by means of square wave control, so that the motor can be operated at a constant power. Therefore, multi-mode hybrid control of a permanent-magnet synchronous motor can be realized.