The carbonate samples studied in this paper were collected from the Mesoproterozoic Gaoyuzhuang Formation in Kuancheng Area，Hebei Province. An analysis of carbon and oxygen isotopes compositions of carbonate demonstrates that the original components of the carbonate have been well preserved. The variation range and average of δ13C and δ18O are respectively －5.03‰～0.07‰，－9.92‰～－4.12‰ and －0.90‰，－6.58‰. It' s all lower than that of Jixian section in Tianjin and Ming Tombs section in Beijing. The results show that，the variation of δ13C value is mainly influenced by the oxidation degree and the buried rate of organic carbon. There is a close relationship between the buried rate of organic carbon and the quantity of the blue green microalgae，and there is a strong positive correlation between the δ13C profile and sea level change in tidal flat environments. The δ18O values are chiefly relevant to sea level change. and there is a negative correlation of them. The Z value is calculated in this study to trace quantitatively the changes of paleosalinity，it’s main variation range is 120～125. The correlation coefficient is 0.68 between the Z value and δ18O，and it is 0.88 between the Z value and δ13C. This means that the Z value reflects changes both of carbon and oxygen isotopes compositions. δ13C and δ18O is closely related to the salinity，and it is same with up and down variation of salinity.