The invention discloses a real-time diagnosis method for the unbalanced fault of the original mass of the rotor at the operating speed of the steam turbine generator set, which belongs to the field of fault diagnosis. By collecting the vibration signal of the rotor shaft of the steam turbine unit, the necessary calculation, analysis and judgment are carried out on the vibration data, the real-time calculation and storage of the power frequency vibration amplitude and phase value of the shaft relative vibration on both sides of the rotor, and the real-time verification of the shaft vibration power frequency vibration amplitude, Judging whether the amplitude of the shaft vibration and power frequency vibration on any side of the rotor is greater than the vibration amplitude threshold; combined with the least square method, the shaft vibration and power frequency vibration data are verified for the stability of the shaft vibration power frequency vibration amplitude trend at the working speed and the operating speed Real-time quantitative calculation and analysis such as the verification of the phase stability of the power frequency vibration phase trend of the lower shaft vibration. Combined with various verification results, automatic real-time online diagnosis of whether the rotor original mass imbalance fault occurs at the working speed of the unit. The invention has the advantages of scientific method, reliable conclusion, automatic real-time on-line monitoring, fault diagnosis and the like.