The invention relates to the technical field of oil and gas exploration and logging. Provided are a method and device for measuring a formation elemental capture gamma ray spectrum. The method comprises: (11) performing moderation on a neutron emitted from a neutron source (37) according to a neutron capture cross section of a test sample; and (12) adjusting a relative location of the test sample with respect to the neutron source (37) so that a standard capture gamma ray spectrum of the test sample is measured and acquired at a location where a thermal neutron flux reacting with an atomic nucleus of the test sample reaches a first predetermined value. The measurement method performs moderation on a neutron source according to neutron capture cross sections of different test samples to measure and acquire elemental capture gamma ray spectra of the test samples, thereby acquiring various formation elemental capture gamma ray spectra with higher accuracy.
