Abstract: According to the outcrop and the analyses of the carbon and oxygen isotopes，this paper discusses the identified
stratigraphic sequence surfaces and the response of carbon and oxygen isotopes for the Ordovician formation of Xishui Region
in Guizhou Prvince，and carbon and oxygen isotopes. The result shows the Ordovician system can be divided six three-order
sequences，which include two I-type and two II-type and two III-type sequence surfaces. In the third-order stratigraphic sequence，
13C in system of the advance of sea and the high water level displays trends of increase and decrease respectively. The
responses of carbon and oxygen isotope can effectively reflect the stacking patterns of parasequences form forth order sequence.
Meter-scale cycle has developed two modes in this area during Ordovician period：one is L–M meter-scale cycle type，and the
other is Subtidal meter-scale cycle type.

Key words: sequence stratigraphy, system tract, Carbon and Oxygen isotopes, Ordovician, Xishui Region