The Xicheng Pb-Zn Orefield, which belongs to the Hercynian Kunlun-Qiling accretionary fold belt, is located in Xihe county, Gansu province. Pb-Zn ore beds are confined to the Devonian sediments of this fold belt. There is a lot of organic carbon in the sediments, and these ore bodies are mainly distributed in the organic-rich strata.Kerogen in carbon-bearing rocks is discussed in this paper. The components of kerogen in this area are mainly vitrinite, exinite, alginite and inertinite, so the kerogen belongs to sopropel-humus type kerogen. The maturity of kerogen differs from place to place in the orefield. By py-rolysis, samples, especially shale samples, studied showed a double S2 signal; in these cases the first of the two peaks can be eliminated by a preliminary chloroform extraction. NSO-compounds were found by the chromatogram analysis; therefore the first peak of S2 may be due to NSO-compounds. It is concluded from the maturity and R0 value of kerogen that several episodes of hydrothermal activities occurred in this area. The ore deposits in the Xicheng Orefield were found by hydrothermal activities.