The Dengyingxia Stage (Late Precambrian) in South China is a marine carbonate sedimentary stage with extensively developed dolostones. The primary dolostones precipitated directly from sea water are developed in the middle unit of Dengying Formation and their primary texture are reserved well. The δ¹³C and δ¹⁸O values have been determined from 40 samples of primary dolomites (dolostones): 13C=3.64‰ and δ¹⁸O=-1.17‰ (n=6) for micrite dolomites; δ¹³C=3.52‰ and δ¹⁸O=-1.86‰ (n=15) for algae dolostones; δ¹³C=2.90‰ and δ¹⁸O=-2.65‰ (n=8) for fibrous dolomite cements; δ¹³C=2.96‰ and δ¹⁸O=-2.41‰ (n=8) for bladed dolomite cements; δ¹³C=2.79‰ and δ¹⁸O=-3.13‰ (n=3) for micrite lamella and fibrous dolomite cements.  The average  δ¹³C and δ¹⁸O values of all 40 samples are 3.25‰±0.44‰ and -2.12‰±0.98‰ respectively (PDB standard). The heaviest δ¹³C and  δ¹⁸O values in overlap ping area of the values of the primary dolomite sediments and the cements in diagram, δ¹³C=4.43‰ [JP](PDB) and δ¹⁸O=-0.62‰ (PDB), has been determined as the primary carbon and oxygen isotope composition of the Dengyingxia marine carbonate. The δ¹⁸O value of sea water of Dengyingxia Age is 2.90‰(SMOW) calculated based on the salinity of the inclusion in primary dolomite cement. The temperature of sea water at that time is 40.8 ℃ calculated on the basis of the primary δ¹⁸O value. It indicates that hot climate and high temperature existed in Dengyingxia Age in South China.