The invention discloses a partial discharge detecting method and system. An appropriate time window length is selected, the amplitudes of pulses in each window are obtained and averaged, the time in each cycle is converted into a phase, and an average discharge amount waveform diagram is generated in combination with the average pulse amplitude and the phase information, so as to realize state detection and fault diagnosis of the partial discharge of equipment finally through identifying the characteristics of the waveform diagram. The partial discharge detecting method can be widely applied to partial discharge detection of various kinds of power equipment; and the influence of noise is removed; therefore, the measurement result is more accurate.