Based on the Sanhui outcrop survey and thin section observation, carbon and oxygen isotopic compositions of 237 Xixiangchi Formation samples are studied in Southeastern Sichuan Basin. The results show that values of δ18 O are relatively stable, mainly from -8‰ to -6‰, with an average of -7.63‰. The variation range of δ13 C values is -5.53‰ ~ 3.44‰. Using the carbon and oxygen isotope to calculate the paleotemperature and paleosalinity , the result show that the Z value is higher than 120‰, the paleotemperature is about at 19℃ to 25℃, and it told us that the sedimentary period is generally in seawatersaline seawater environment, which was a warm or hot subtropical climate. It was considered that there are five sea level change stages during sedimentary period: slowly transgression and regression in early, rapid transgression in middle, slow regression in latemiddle time, fluctuation in late, regression in the end. The reservoir rock for Xixiangchi formation in Sanhui section are mainly dolomite, the revisor space is composed of dissolution pores intergranular pores and intergranular pores. The decline of multistage sea level corresponds to the negative drift of carbon isotope, thus developed a multi cycle prosodic stratigraphic formation that is upward and shallow, forming multiple sets of reservoirs in the vertical. The formation and evolution of the reservoir for the Xixiangchi Formation was controlled by the change of sea level, mainly in the upper paleogomorphology and the upper part of the shallow cycle. In addition, based on the significant positive of δ13 C value, the bottom boundary of the Furong formation is clearly defined, which provides evidence for the division of Cambrian strata in the Sichuan basin.