The red carbonate rock is a kind of representative sedimentary rock with purple- red colors of the Ordovician in South China, and may contain special palaeoenvironmental information. There is a well exposed thick red carbonate rock section in the Sanbaidong area of Xiangxi, which is mainly developed in the Dawan Formation and the Guniutan Formation. This paper studied 355 carbon- oxygen isotope, Mn- Sr element samples and 10 conodont samples on it. According to the restriction of conodont samples from these formations, the bottom boundary of the Dawan Formation may be near the top boundary of the Florian Stage, the boundary between the Dawan Formation and the Guniutan Formation may be in the lower to middle part of the Darriwilian Stage, and the top boundary of the Guniutan Formation is near the top boundary of the Darriwilian Stage. With δ13C- δ18O correlation analysis and Mn- Sr element evaluation, it is considered the samples are not strongly affected by diagenesis. 355 samples show that the δ13C and δ18O of the Sanbaidong section are low amplitude and high frequency fluctuations. The δ13C are between 0.38‰ to 1.67‰, while the δ18O are between 9.34‰ and 7.21‰. Among them, BDNICE and MDICE are two global isotopic events that can be compared with this section, and LDNICE can be compared indirectly. In addition, there are two unnamed δ13C isotope shifts with potential comparative value. In general, there is an increasing trend of δ13C from east to west along the equator on the north Gondwana. The fluctuation amplitude in South China is generally smooth, which may have been caused by the difference in bottom seawater stratification in different blocks during the seawater circulation. Based on the δ13C and δ18O calculation, the red carbonate rocks should contain marine characteristics with middle to high palaeosalinity that increases upwards. Combined with the lithology, color, palaeontological quantity of the section and regional palaeogeography, it is believed that there may be an oxidation event at the bottom of the Dawan Formation, and the red carbonate rocks may be the product of the temporary relative sea level decline superimposed oxidation events.