The invention discloses a method and device for diagnosing power generator discharge faults according to noise characteristic frequency bands. A plurality of noise measurement points are distributed on the upper portion of a power generator stator, preset sound frequency bands (1000-6000 Hz) of noise signals of each noise measurement point are extracted to serve as the characteristic frequency bands of discharge faults of a power generator, and accordingly whether discharge faults exist close to the obtained measurement points are analyzed. The method and device have advantage that under the condition that operation of the power generator is not affected, the discharge faults of the power generator are quickly and accurately diagnosed. The scheme is simple and practical, and operation is convenient. Meanwhile, investment is little because an existing noise recorder or recording equipment can be used. Faults of a generator set can be comprehensively monitored.