The limestone units at the base of the Shangsi Formation (Lower Carboniferous) in Huishui, South Guizhou are about seven meters thick containing five meters coral framework reef sandwiched by the bioclastic limestones of bank facies. Four microfacies types are distinguished based on the fossil compositions, grain sizes, structure as well as texture. They are ① wackestone; ② packstone; ③ coral bafflestone; ④ stromatoporoid coverstone. The bank limestone units are mainly composed of packstones including bioclasts of coral, brachiopod, calcareous algae, ostracod and crinoid. High breakage and poor sorting of the bioclasts are palaeoenvironmental proxies of very rapid deposition after long distance or/and mutiple transportions under strong hydrodynamic conditions. Bank environment is not suitable for coral blooms where solitary rugose corals and small sized colonial rugose corals are sparsely occurred. The reefal units are majorly comprised of wackestones and coral bafflestones with minor stromatoporoid coverstones and algae bindstones. The occurrences of brachiopod, calcareous algae, foraminifera, crinoid, ostracod, gastropod, bryozoan and stromatoporoid illustrate a high biodiversity ecosystem. In aspect of organic abundance, they are not abundant of supporting each other. Meanwhile, micritic components are rich as matrixes. Such a lithological feature suggests that a weak hydrodynamic condition is idealized for the expansion of coral communities of solitary rugose corals, Syringopora and Siphonodendron, and then formation of in situ reef limestones.