A method of monitoring a temperature of a rotor of a permanent magnet synchronous motor, comprising: Acquiring, an a-phase line current of a stator of a permanent magnet synchronous motor as a first line current; Acquiring, a b-phase line current of the stator as a second line current; Acquiring, a line voltage between the a-phase and the b-phase of the stator; Acquiring, a rotating speed of a rotor of the permanent magnet synchronous motor; Substituting, the first line current, the second line current, the line voltage, the rotating speed, an inductance parameter of the permanent magnet synchronous motor and a temperature characteristic equation of a permanent magnet of the rotor into a preset rotor temperature expression, to calculate the temperature of the rotor, characterised in that: the temperature characteristic equation is acquired by steps of: measuring and recording a current ambient temperature as a first rotor temperature under a condition that the permanent magnet synchronous motor is in a complete cold state; dragging the permanent magnet synchronous motor to a rated rotating speed in an open-circuit state, and measuring a line voltage of the permanent magnet synchronous motor as a first line voltage; running the permanent magnet synchronous motor to rated power, and measuring a temperature of the stator of the permanent magnet synchronous motor as a second rotor temperature after the temperature of the permanent magnet synchronous motor is stable; after measuring the second rotor temperature, making the permanent magnet synchronous motor unloaded and keeping the permanent magnet synchronous motor running at a rated rotating speed, and measuring a line voltage of the permanent magnet synchronous motor as a second line voltage; and deriving the temperature characteristic equation from the first rotor temperature, the first line voltage, the second rotor temperature, the second line voltage and the rated rotating speed. Acquiring, an a-phase line current of a stator of a permanent magnet synchronous motor as a first line current; Acquiring, a b-phase line current of the stator as a second line current; Acquiring, a line voltage between the a-phase and the b-phase of the stator; Acquiring, a rotating speed of a rotor of the permanent magnet synchronous motor; Substituting, the first line current, the second line current, the line voltage, the rotating speed, an inductance parameter of the permanent magnet synchronous motor and a temperature characteristic equation of a permanent magnet of the rotor into a preset rotor temperature expression, to calculate the temperature of the rotor, characterised in that: the temperature characteristic equation is acquired by steps of: measuring and recording a current ambient temperature as a first rotor temperature under a condition that the permanent magnet synchronous motor is in a complete cold state; dragging the permanent magnet synchronous motor to a rated rotating speed in an open-circuit state, and measuring a line voltage of the permanent magnet synchronous motor as a first line voltage; running the permanent magnet synchronous motor to rated power, and measuring a temperature of the stator of the permanent magnet synchronous motor as a second rotor temperature after the temperature of the permanent magnet synchronous motor is stable; after measuring the second rotor temperature, making the permanent magnet synchronous motor unloaded and keeping the permanent magnet synchronous motor running at a rated rotating speed, and measuring a line voltage of the permanent magnet synchronous motor as a second line voltage; and deriving the temperature characteristic equation from the first rotor temperature, the first line voltage, the second rotor temperature, the second line voltage and the rated rotating speed. measuring and recording a current ambient temperature as a first rotor temperature under a condition that the permanent magnet synchronous motor is in a complete cold state; dragging the permanent magnet synchronous motor to a rated rotating speed in an open-circuit state, and measuring a line voltage of the permanent magnet synchronous motor as a first line voltage; running the permanent magnet synchronous motor to rated power, and measuring a temperature of the stator of the permanent magnet synchronous motor as a second rotor temperature after the temperature of the permanent magnet synchronous motor is stable; after measuring the second rotor temperature, making the permanent magnet synchronous motor unloaded and keeping the permanent magnet synchronous motor running at a rated rotating speed, and measuring a line voltage of the permanent magnet synchronous motor as a second line voltage; and deriving the temperature characteristic equation from the first rotor temperature, the first line voltage, the second rotor temperature, the second line voltage and the rated rotating speed.