The invention discloses a one-point grounding protection circuit for a brushless excitation generator rotor winding. The one-point grounding protection circuit comprises a first sampling control circuit, a second sampling control circuit and a sampling resistor, wherein the first sampling control circuit comprises a first switch; the second sampling control circuit comprises a second switch; the first sampling control circuit is connected with the second sampling control circuit in parallel; a first common end is connected with the negative electrode of the r generator rotor winding; a second common end is connected with the first end of the sampling resistor; the second end of the sampling resistor is connected with the access end of the rotating shaft of the generator rotor; an additional direct current injection power supply is not required; and an auxiliary circuit without the additional direct current power supply is adopted by the negative electrode of the brushless excitation power generator rotor winding, so that the reliability of the protection apparatus is improved, and the calculation precision is improved. The invention also discloses a one-point grounding protection apparatus and method for the brushless excitation generator rotor winding.