Abstract: Authigenic clay minerals are controlled by, and therefore indicative of, physiochemical conditions of the diagenetic process. In oil and gas exploration, timely acquisition of the information on clay minerals and hydrocarbon is of direct application value in terms of understanding the evolution process and diagnosing the existence of hydrocarbon. The experimental work reported in this paper has shown that near-infrared reflectance spectroscopy is useful for extracting the information on hydrocarbon present in a mi-nor to trace amount in sedimentary rocks and detecting the fact that the spatial variations of a series of clay minerals such as (ammoni-um-bearing) illite, chlorite and kaolinite can directly reflect the changes in temperature and pore fluid composition during the diage-netic process. The results obtained by the authors, therefore, will contribute to improving the understanding of environmental condi-tions and thermal maturity of organic matter in diagenesis.