The invention provides a double-channel microwave signal automatic zeroing device for micro discharge effect detection. After forwardly/reversely coupled signals are input, the signals are divided by a bridge into two parts, wherein one part is transmitted to a power monitoring module to perform parameter monitoring, and the other part is transmitted to an amplitude modulation and phase modulation channel to perform zeroing; after the signals enter the amplitude modulation and phase modulation channel, the two channels of signals are adjusted by a digitally controlled attenuator to be consistent in amplitude according to power detection data; and after the two channels of signals are made consistent in amplitude, the signals pass through a digitally controlled phase shift and enter an in-phase combiner for signal synthesis, and signal phase adjustment is carried out with the help of a zeroing signal amplitude monitoring module. The reliability of the automatic zeroing device of the invention is improved exponentially, and the service life is prolonged exponentially. No additional power meter is needed, the system structure is simplified, and the reliability of the system is improved to a certain extent. Moreover, human operation error is avoided because of the automatic zeroing function, and the effectiveness of micro discharge effect detection is guaranteed.