The invention discloses a controllable-neutron three-detector element well logging device and method, which specifically relate to the field of oil and natural gas exploration. The device uses a D-T controllable neutron source, a near He-3 neutron detector, a LaBr3 crystal gamma detector, and a super far He-3 thermal neutron detector. The two He-3 neutron detectors collect the time spectrum of neutrons and the total count of neutrons. The LaBr3 gamma detector collects inelastic and capture gamma time spectrums, and measurement information is uploaded to ground equipment through a telemetry pipe nipple of the instrument. The method includes the following steps: first, processing the inelastic gamma energy spectrum, calculating the inelastic gamma yield of elements, and calculating the dry weights of Si, C and other elements according to the inelastic yield of elements, the near-to-super far neutron counting ratio and other information; and then, processing the capture gamma energy spectrum, calculating the capture yield of elements, and calculating the contents of elements which can be measured by the capture gamma energy spectrum, such as Ca, S and Fe, according to the contents of elements determined by inelastic gamma and the capture yield.