The inter-turn short circuit of field winding in synchronous generator may cause mechanical vibration，and the study of the electromagnetic torque during the fault will set the foundation for characteristics analysis on the mechanical vibration.The electromagnetic torque in case of field winding short circuits is calculated based on multi-loop mathematical model.In the calculation，the complex interactions of different kinds of components of air-gap magnetic fields，including the space fundamental and harmonics，produced by stator and rotor windings and rotating in different directions with various speed，are taken into consideration.Then the experiments on a12kW synchronous generator with three pairs of non-salient pole are carried out，and the results are consistent with the calculation.Furthermore，theoretical analysis on the electromagnetic torque characteristics is made，according to the harmonic characteristics of the stator and rotor fault currents as well as the magnetic fields excited by all the currents.The paper provides some insight into the influence of the inter-turn short circuits of field windings upon the electromagnetic torque，and it also offers a basis for utilizing mechanical vibration characteristics in fault monitoring.