Abstract: The coral reefs along the Leiqiong Coast in the northern part of the South China Sea are key indicators for studying paleo-sea level changes. However, due to the lack of unified standards, significant spatiotemporal discrepancies exist in coral-derived sea-level data. In this study, through field measurements of the top surface elevation of 27 modern Porites microatolls in the coral reef area of eastern Hainan Island, the sea level indicative meaning of Porites microatolls was first precisely quantified. Meanwhile, 65 published sea-level index proxies based on U-Th dated fossil Porites (microatoll) corals from the region were systematically recalibrated and integrated to reconstruct a more accurate and reliable sea-level change history during the Middle Holocene in the northern South China Sea. The research reveals that those modern Porites colonies with dead upper surfaces but intact overall viability have reached their growth limits. Their top elevation lie 146.09 cm below the mean tide level of Qinglan Port and 15.09 cm below the lowest low water, and the height differences of the growth limit is only ±8.35 cm, representing a typical developmental pattern of Porites microatolls. It is confirmed that their growth limits are primarily controlled by the lowest low tide level, and they are ideal indicators for reconstructing past sea levels. Sea level reconstruction results indicate that the relative sea level in the northern South China Sea exhibited a fluctuating downward trend from 6143 ±34 cal a BP to 3013 ±9 cal a BP, ranging from 25 ±9.8 cm to 136.09 ±9.8 cm. Comparison with sea level records from surrounding South China Sea regions reveals spatiotemporal variations in the timing and magnitude of mid-Holocene high sea-level, which may be attributable to differences in indicator elevation estimation methods and dating techniques. In addition, a comparison of the research results with the sea level predicted by the GIA model (ICE-6G_HetML14), reveals that the mid- and late-Holocene sea-level data at three locations along the Leqiong coast are all below the model curve. This indicates that these regions may have undergone tectonic subsidence over the past several thousand years. The results of this study offer an important scientific basis for predicting the future sea-level change trend in the northern South China Sea, and provide a new perspective on regional tectonic evolution studies.