Abstract: The C and O isotopes of the Middle Cambrian of the Xiaweidian Section in the Beijing Western Mountain areas is for the first time reported by our study. In order to study the evolutionary history of the Middle Cambrian of Xiaweidian Section and its controlling factors, sedimentary characteristics and stable isotopes are applied to establish stratigraphic sequences based on the chronology framework established by eustatic sea level changes. Three 2^nd order and eight 3^rd order sequences are recognized. The sedimentary facies observed include evaporated tidal flat, low-energy inner platform, high-energy outer platform and low-energy shallow sea. The eustatic sea-level change is the primary driving factor which controls the sequence development in a tectonic stable and warm climate background as such.