The technique of elemental logging is a general designation of a set of nuclear logging for measuring in-situ the element concentrations in formation and transferring them to the mineral contents. This paper has made a fully introduction to the principles and methods of natural gamma-ray logging, activation logging, thermal neutron capture spectrometry and induced neutron gamma-ray inelastic scatter spectrometry to determine the element concentration in scientific drilling project. And a detail discussion has been made for how to select and establish the models of transform relations from element concentrations to mineral contents in accordance with the geological lithostratigraphy. Finally, some application examples of the elemental logging technique in the KTB and ODP are presented. It is indicated that the elemental logging technique may play an important role in the following fields: the reconstruction of lithological section, the research of the variation about element concentrations and mineral contents, the study on the geochemical process of mineral alteration in the condition of high-temperature and high-pressure, the identification of lithological inhomogeneity, and the reconstruction of geochemical section, etc. Furthermore, the elemental logging technique can also be used to derive accurately the porosity and permeability from the calculation of the matrix density, to make correlation between wells, and to provide the lost information resulted from the incomplete coring or cutting collection, etc.