The invention discloses a calculation method of a rotating speed Omega of a generator rotor in a power system stabilizer (PSS4B) method. With the adoption of the calculation method, the calculation amount in the implementation process is small, the implementation is flexibly and conveniently carried out through an excitation regulator, a simple and effective way is provided to realize PSS4B through a generator excitation regulator, and the calculation method is belongs to the field of control of power systems; the calculation method can be applied to a hydroelectric power station or a thermal power plant, a wind power plant, etc.