The invention relates to a method used for tracking the rotating speed of an electric motor through a frequency converter. The method comprises the following steps: firstly, the frequency converter is controlled to output currents with the set frequency, and the amplitude of the output current is fixed; secondly, according to the output frequency of the frequency converter, the voltage value of the V/F curve of the electric motor is calculated; thirdly, whether the output voltage of the frequency converter is larger than or equal to the voltage value of the V/F curve of the electric motor is judged, if yes, the step four is carried out, and if no, the step five is carried out; fourthly, the output voltage and the output frequency of the frequency converter are maintained to be unchanged, and the search is finished; and fifthly, the set frequency is changed, and the step one is executed. The invention also provides a corresponding device. The invention cuts the cost of a rotating speed tracking circuit out, improves the reliability of a system, and enables the system to have obvious advantages in cost and reliability.