Diagenesis and its corresponding cements are extensively developed in the upper Carboniferous phylloid algal reef and circumjacent limestone of Bianping Village, Houchang Town, Ziyun County. These cements are prominent and representative in Houchang Town. A study of crystal shape, fabric and cathodoluminescence images of cements as well as the contacts between cements can help determine paragenetic sequences, recognize diagenetic environments, and understand the porosity evolution in the phylloid algal reef limestones. During the syndiagenetic stage, wackestone and packstone sediments generally had low porosity and permeability, pores were filled with sea-floor micrite cement, biological encrustation and sea-floor cementation sediments rich in the fragments of phylloid algal thalli had high porosity and big pores, and marine botryoidal cement and isopachous acicular cement grew in the pores. During the early diagenetic stage, cementation supplied a great amount of cements, constructed rock framework, and consequently decided the features of the limestone rock. Blocky calcite spar and calcite microspar were formed in small pores, and radiating cement fans grew in big pores. During the epidiagenetic stage, extensive dissolution and cementation occurred. Vuggy or channel porosity was created by dissolution in the recharge area, and calcite precipitation was greatly increased in downflow areas. Meteoric phreatic cements include isopachous columnar calcite and blocky or equant calcite cement. Isopachous columnar cement is volumetrically more abundant. The porosity of the reef limestone was reduced dramatically through the early-stage cementation, so the reef limestone could prevent mechanical compaction. During the middle and late diagenetic stage, nearly all porosity was occluded by cements with low rates of fluid influx and efflux, and the remaining pores were filled with isopachous bladed cement and drusy or blocky calcite spar. Some preexisting cements were altered during the middle or late diagenetic stage, the color of isopachous bladed to columnar calcite cement changed from gray to white, and the color of botryoidal cement became more blackish due to hydrocarbon infiltration. Some isopachous bladed to columnar calcite cement could be dissolved, leaving mouldic pores filled subsequently and radiating cement fans formed simultaneously. Construction fracturing is one of the main types of diagenesis during the catagenesis stage. Rusty microcrystalline layers containing Fe₂O₃ line the wall of some fractures, and vadose pisoids and ferrugineous crystal silt containing Fe₂O₃ are deposited at the bottom of the cavities formed in the tectonic fractures, which indicates that they were formed in oxidizing vadose environments. Late-stage fractures are filled with coarse-grained white or green bladed and drusy or blocky calcite spar. The middle part of some of these fractures is filled with bitumen block. A reason for the phylloid algal reef limestone not becoming oil and gas reservoirs might be that the pores of the phylloid algal reef limestone were filled with cements before or during the late diagenetic stage, and no large interconnected secondary pores were created afterwards. Only limestone that has a great deal of secondary porosity generated during the catagenesis stage could become oil and gas reservoirs in the Nanpanjiang Basin.