Abstract: Reef corals are perfect materials for reconstructing high-resolution paleoclimate records. The microstructures of reef coral provide detail information of their growth, and are very important for us to understand the paleoclimate records reconstructed on corals. In this paper, we analyze the microstructures of some modern and mid-Holocene Porites corals from Beihai and Sanya in the northern South China Sea using Scanning Electron Microscope (SEM) method, and seek for microstructures that can be used for paleoclimate reconstructi septa, spine, pore, di types of aragonite crys on. The microstructures observed at ssepiment, coenosteum and synapticu tals(shingle, cluster, pillar and needle low magnification (<1 000) are:corallite, lae. At high magnification (≥ 1 000), four), and centers of calcification (COCs) are observed. With the help of these microstructures, the boundaries of death-growth recovering are easily identified. No death-growth recovering boundary has been found during the periods of extreme cold winters and extreme warm summers in most of the samples from Sanya and Beihai, indicating that Porites corals may grow continuously through the whole year in these two regions. However, several death-growth recovering boundaries were found and recovery events for Porites extremes may account for them. and measuring distance between in some modern Porites corals from Beihai, indicating several extinction corals in recent years in this region. Some other factors rather than SST By counting on the numbers of dissepiments within annual growth bands dissepiments, we found that the time for concreting materials between two dissepiments was about one month. Therefore, the dissepiments in Porites may indicate monthly bands, which is valuable for reconstructing paleoclimate records of higher-resolution. Extraneous materials were found to fill in the dark bands of some fossil Porites corals from Beihai. Coupled with the X-ray microstructures and oxygen isotopes, the high-density bands.