The invention discloses an automatic peak stabilizing method for a pulsed neutron energy spectrum. The automatic peak stabilizing method comprises the steps that a pulsed neutron energy spectrum logging instrument is conveyed to the target layer through a cable, a ground power supplying downhole neutron generator emits neutrons, a receiver receives a neutron attenuation energy spectrum and transmits the neutron attenuation energy spectrum to the ground through the cable, and in the actual measuring process, a gamma energy spectrum measured through the instrument can drift due to environmentalfactors such as the well temperature, the cable length and signal attenuation. By automatically stabilizing the peak value, the downhole voltage regulation function can be realized through peak valuechange, automatic peak value locking is achieved, the data accuracy is guaranteed, and the test efficiency and the success rate are improved.