The inter-turn short circuit in field winding is one of the common faults of synchronous generators. To ensure the safe and reliable operation of the generator unit and the power grid, it is necessary to detect this kind of fault on-line. We firstly introduced the status quo of current research methods for the on-line detection of inter-turn short circuit faults in field winding of synchronous generators, including the magnetic-current harmonics analysis method, the probing coil method, the multi-loop method, the output electrical parameter analysis method and the vibration analysis method. These methods and their diagnostic effects were discussed and compared. Then, two new ideas for the output electrical parameter analysis method were provided and the developing tendency of on-line detection methods was forecasted. Finally, it was pointed out on-line analysis method should be practical and multi-functional.