The invention relates to the technical field of frequency converters, in particular to a frequency converter with the rotating speed tracking function and a rotating speed tracking method with the frequency converter. The frequency converter comprises a sampling circuit, an amplification adjusting circuit, a shaping circuit and an isolation output circuit, wherein the sampling circuit is connected with any two phases in an output circuit of a motor, and the amplification adjusting circuit, the shaping circuit and the isolation output circuit are sequentially connected according to the circuit flow direction sequence. In the amplification adjusting circuit, after difference amplification and waveshape conversion are carried out on residual voltage signals, shaping is carried out through the shaping circuit, and the frequency of pulse signals is calculated by controlling a processor. The residual voltage frequency of the motor is detected and processed through a hardware circuit to obtain the more accurate voltage value, then the voltage value is utilized for achieving rotating speed tracking of the motor, and the rotating speed of the motor is obtained. Due to the fact that the residual voltage signals of the motor can be directly obtained from the motor, repeated attempts are not required, the reaction time is greatly shortened, the impact caused by a current to equipment is also reduced, efficiency is greatly improved, misinformed current faults of the equipment are reduced, and the service life of the equipment is prolonged.