The invention discloses a method for measuring and calculating the rotation speed of a rotor of a wind driven generator. The method comprises the following steps of: sampling current signals on a variable propeller motor at a certain sampling frequency; acquiring spectrum distribution of the current signals; determining a peak value of the spectrum distribution; and calculating the rotation speed of the rotor according to the peak value. A machine-readable recording medium and a computer program are used for implementing the method. The invention also discloses a system for measuring and calculating the rotation speed of the rotor of the wind driven generator. The system comprises a sampling module, a spectrum module, an analyzing module and a calculating module. By the method and the system for measuring and calculating the rotation speed of the rotor of the wind driven generator, additional sensors or other hardware is not required to be mounted, so that the cost is saved, and the structure of the wind driven generator is simplified.