Abstract:Objectives:Phylloid reefs are found in the Middle Permian Yangxin Formation in Huize County, Yunnan Province, based on the 1∶50000 regional geological survey. Their microfacies characteristics and sedimentary model is studied in this paper.Methods & Results: By the way of detailed microfacies analysis, Seven carbonate microfacies types are identified as follows: bioclastic (foraminifers and algae) grainstone containing oncolites, bioclastic (foraminifers and algae) grainstone, phylloid algal reef limestone, bioclastic (brachiopods and echinoderms) packstone, bioclastic (echinoderms and algae) packstone, bioclastic (ostracods and echinoderms) wackestone and bioclastic (algae) wackestone. Four sedimentary subfacies were determined, which are relative deep interbank subfacies, lowenergy bioclastic bank subfacies, phylloid algal reef subfacies and highenergy bioclastic bank subfacies.Conclusions: Phylloid algal reefs formed in the lower part of highenergy bioclastic bank subfacies, resulting from relative sealevel rise. Profile Luoshuidong section may develop in an open carbonate platform environment, indicating the northeastern Yunnan was in a warm palaeoclimatical environment during the Middle Permian.