The study area is located in the northeast of the North China Craton and geographically belongs to the middle and northern Yanshan area. In this area,Mesoproterozoic and Neoproterozoic strata are well developed and constitute the type section of Mesoproterozoic and Neoproterozoic strata in China. Over ten thousand meters of Mesoproterozoic and Neoproterozoic strata recorded paleogeography and paleoenvironment, paleo_ocean geochemistry and the history of life development and sedimentary evolution. The Kuancheng area of northern Hebei has great thickness of Mesoproterozoic and Neoproterozoic sediments, with ideal outcrops. Previous researchers had conducted fairly detailed investigation in this area. Geochemical studies of Mesoproterozoic and Neoproterozoic strata in Jixian County started in the late 1970's, with the emphasis placed on major elements. In the middle of the 1980's, Liu Baoquan et al. (1985) carried out organic geochemical researches on Mesoproterozoic, Neoproterozoic and Lower Paleozoic carbonate rocks in North China. Wang Songshan et al. obtained an age of dark banded chert (1317 Ma) at the top of Yangzhuang Fomration. The multiple stratigraphic division method was also introduced into the division and correlation of Mesoproterozoic and Neoproterozoic strata.The Yangzhuang formation has a total thickness of 322.37 m and consists mainly of carbonate rocks which include micritic dolomite, sand-bearing micritic dolomite and chert striped dolomite as well as local corrugated stromatolite dolomite, arenaceous dolomite and gravel lithic silicalite. In these rocks, horizontal laminae and birdeye structures are widespread. In order to analyze the influence of geochemical characteristics of carbonate rocks on stratigraphic and sequence boundaries as well as sedimentary environment, the authors chose the geological section of Mesoproterozoic Yangzhuang Formation in Kuancheng to conduct in-situ measurement. Along this section, there exists obvious vertical characteristic evolutionary regularity of major and trace elements as well as carbon and oxygen isotopes, which is especially obvious near stratigraphic and sequence boundaries. CaO content is 21.07%～16.45% from 1st Member to 2nd Member of Yangzhuang Formation, and is 16.45%～24.21% from 2nd Member to 3rd Member. From the bottom of Yangzhuang Formation upward, Sr changes abruptly from 44.59 μg/g to 98.16 μg/g and Ba from 0.51 μg/g to 10.45 μg/g, whereas δ13C and δ18O vary in the ranges of 0 ‰ to -1.5‰ and -3.5‰ to -8.5‰, respectively. The variations of the above data were basically consistent with the sea level variation of the same period, suggesting that geochemical characteristics can serve as indicators for dividing stratigraphic or sequence boundaries and, especially, for optimizing these boundaries. δ18O values of carbonate rocks formed in the same sedimentary and diagenetic environment are closely related to the physical-chemical conditions of the sedimentation period and, especially, to the climatic variation. It is generally held that in the glaciation period, temperature dropped, salinity rose, and some light oxygen isotopes were trapped in the glacial sheet, causing the relative increase of δ18O values in the sea water, whereas in the temperature-rising period, glacial sheet was melted, salinity decreased, and large quantities of light oxygen isotopes were released, which would result in the relative increase of the δ18O values in the sea water. Carbon and oxygen isotopic data in this paper demonstrate that, although there exists a slight positive bias in 2nd Member of Yangzhuang Formation, C isotopes generally show a relatively stable variation and have negative values, varying in the range of -0.55 ‰ to -1.28 ‰. Oxygen isotopes vary in the range of -8.17‰ to -3.47‰, generally assuming an obvious positive bias trend.The considerable vertical fluctuation of major and trace elements in Yangzhuang Formation of this area indicates brisk tectonic activities of the Yanshan aulacogen in this period, which led to the remarkable variation of sedimentary environment. Oxygen isotope analyses suggest that the paleoclimate was basically in a sedimentary environment of supralittoral zone with relatively high temperature. Major and trace elements at stratigraphic and sequence boundaries change evidently, and the variations of carbon and oxygen isotoles assume a corresponding relationship with the rise and fall of the sea level. All this suggests that geochemical characteristics can be used to joptimize stratigraphic or sequence boundaries that have already been defined.