An electric motor rotor, an electric motor, and a direct current variable frequency compressor are provided. A magnetic beam finishing groove is added on the rotor core of the electric motor rotor, sothat a magnetic bridge is formed between the magnetic beam finishing groove and the magnetic isolation groove, and the distance between the magnetic beam finishing groove and the magnetic isolation groove causes the magnetic bridge to be magnetically saturated, and then the magnetoresistance increases significantly, close to air magnetoresistance. According to the principle of minimum magnetoresistance, that is, the flux is always closed along the path with the smallest magnetoresistance, magnetic lines of force will be confined to the magnetic bridge. At this time, the magnetoresistances ofthe magnetic beam finishing groove, the magnetic bridge, and magnetic isolation grooves are equivalent, which co-determine the polar arc coefficient, so that on the basis of ensuring the mechanical strength of the magnetic isolation bridge between the magnetic isolation groove and the edge of the rotor core, the pole arc coefficient can be set in a larger range, the optimal pole arc coefficient can be designed, and the optimal pole arc coefficient can be obtained, the harmonic distortion rate of the no-load back electromotive force, the tooth groove torque and the torque ripple can be reduced,the motor control ability is improved, and the motor noise vibration is reduced.