Abstract: The Cambrian-Ordovician boundary section at Changshan is one of the well-established sections in stratigraphic region of North China. Zhou and Zhang (1978) studied the trilobites in detail across this boundary in Zhaogezhuang area. They discovered conspicuous difference in trilobite fauna cross the Cambrian-Ordovician boundary (between bed 6 and bed 7 at Changshan section). This paper deals with the variation of isotopes (δ13C and δ18O) and trace elements across the Cambrian-Ordovician boundary at same section. The authors discovered that, besides the conspicuous difference in trilobite fauna, there is also variance at different ranges in isotope compositions and almost all trace element contents across the Cambraian-Ordovician boundary in Changshan section. This indicates the change of sedimentary environment in that time. Based on the analyses of C and O isotopes it is concluded that the carbonate rocks from the strata across the Cambrian-Ordovician boundary in Changshan section were formed in submarine environment.