This article conducts carbon and oxygen isotopes, rare earth, and trace element geochemical analyses of carbonate samples from the Triassic Sanhedong Formation in the Hexi Area of the northwest Yunnan Province. The analyzed results demonstrate that their carbon and oxygen isotope values are consistent with the normal marine carbonate rocks. Samples from the Sanhedong Formation have a high Sr and Ba content, low Co, Cu, Th, U, Ho and total rare earth element content, and a negative anomaly of Eu, but they are slightly enriched in light rare earth elements. Paleosalinity parameter Z value, and Sr/Ba, Sr/Cu and Rb/Sr ratios indicate that they deposited in a marine saline water environment with dry-hot climate. The ratios of Cu/Zn, V/Cr, Ni/Co and U/Th indicate an anoxic environment. Y/Ho, δCe and δEu values indicate that the limestone of the Sanhedong Formation is less affected by diagenesis during sedimentation. These characters are similar to that of the Xujiahe Formation in the northern part of the Sichuan Basin, indicating that the Lanping Basin and the Sichuan Basin in the Upper Yangtze Plate probably have a similar tectonic and sedimentary environment during Late Triassic, which can help to study the paleoenvironment and tectonic attributes of the Lanping-Simao Block.