Abstract: Ordovician organic reef discovered in the Lunnan area at the first time was examined in terms of paieoecology, and then 4 hermatypic communities were established, i. e. Calathium-Archaeoscyphia, Palaeoporella, Cyanophyta and Calcisponge. Their composition, texture, function . and habitat were also examined. Analysis of evolution of hermatypic community shows that two phases of community alternations occur in the course of formation of Ordovician organic reef, i. e. Calathium-Archaeoscyphia → Palaeoporella → Calathium-Archaeoscyphia and Gyanophyta → Calcisponge. The former phase corresponds to early, peak, and late baffling periods in the evoiutionary course of Early Ordovician organic reef, whereas the latter phase corresponds to the bounding and baffling-bounding periods during the evolution of Late Ordovician organic reef.

Key words: Tarim basin, Lunnan area, Ordovician, Fossil reef, Paleoecology, Paleontological community