Abstract: Abstract：On the basis of carbon and oxygen isotopic compositions of 69 dolomite samples collected from three sampling points of the Sinian Dengying Formation in Sichuan basin and the effectiveness evaluation of the data, the authors studied the changing characteristics of carbon and oxygen isotopes with the purpose of further reconstructing the corresponding paleo-ocean environment and investigating its geological meaning. The δ13C values of dolomite in Dengying Formation vary from -2.85‰ to 4.44‰ with a mean value of 1.80‰ and the δ13Cvaries vary between -9.02‰ and -1.90‰, -5.42‰ on average. The changing trends of the carbon and oxygen isotopes are similar to those in other strata of the same period in the Yangtze platform. Through the reconstruction of paleo-ocean environment, the authors found that the Sichuan basin of Late Sinian Dengying period was in a marine environment, and the seawater temperatures varied mainly between 15℃ and 30℃, suggesting a warm or hot subtropical climate. The sea level experienced six stages in Dengying period in the study area, i.e., slow transgression, lowstand oscillatory regression, highstand oscillatory regression, transient transgression, sustained regression and oscillatory regression. Under the influence of sea level fluctuation, climate change, tectonic movement and volcanic activity, four negative δ13C anomalies (N1~N4) and two positive δ13C anomalies (P1~P2) occurred in dolomite of Dengying Formation. The basin was filled with easily-recognized grape-sized algal dolomite in Deng2 Member, dark clastic rock in Deng3 Member and algal dolomite in Deng4 Member because of the influence of the paleo-ocean environment.