Abstract: In order to diagnose field winding short-circuit fault within turbine generators quickly and accurately, based on the expressions of turbine generator electromagnetic and reactive power, this paper analyzed the variation of generator operating points after a short-circuit fault. With the aid of proportional relationships between the no-load electromotive force and the excitation current, the electromagnetic power and reactive power calculation models were established when the field winding was normal, which were used for the calculation of their expectations, and the measured electromagnetic power and reactive power were compared with the expectations. When the deviation exceeds a certain value, the field winding short-circuit fault within the turbine generator is recognized, and the fault examples demonstrate the effectiveness of this method. The method is a non-invasive on-line monitoring method with high sensitivity. No matter the generator runs at lagging-phase, leading-phase or modulating-phase states, the field winding short-circuit fault can be effectively diagnosed.