About 4000 sediment samples have been grabbed from the bottom of the northern South China Sea to further understanding distribution and sources of heavy metals. Grain sizes of all samples have been measured by the composition of Mastersizer 2000 and sieving method, the content of heavy metals for more than1000 samples have been tested by ICP-AES (samples from Pearl River Estuary) and ICP-MS (samples from other parts), and the distribution and relationship between the content of four heavy metals (Cu, Pb, Zn and Cr ) as well as the mean of the grain size have been analyzed. The results indicate similar distribution of four heavy metals (Cu, Pb, Zn and Cr), with relative high values are mainly came from the Pearl River Estuary declining to the west. Compared to the Chinese first-class sediment standard, regions of above-standard Pb and Zn are mainly distributed in the Pearl River Estuary and offshore to the west of Hailing Island. Above-standard of Cu and Cr values are distributed from Pearl river estuary to Yangjiang sea area alongshore, and above-standard Cr is also distributed widely in Beibu Gulf. There is a strong correlation between the four heavy metals, indicating that the elements have the same origin, with the gradient indicating the source up the Pearl River. We also found four heavy metal enrichment areas in the northern South China Sea alongshore area, and analyzed the source and formation mechanism combine with the ocean currents in this region. We conclude that the heavy metals around Qiongzhou Strait mainly derive from Pearl River, with the most distal deposits to the east of Beibu Gulf. Pollution characteristics and ecological risk have been evaluated by the Hakanson potential ecological risk model. The results show that there are three middle level risk areas in the studied region, which spread mainly from the Pearl River Estuary to the west of Hailing Island.%为全面了解南海北部近海沉积物中重金属的分布及来源，在珠江口至北部湾海域进行了密集的采样工作，然后对4000多个表层沉积物进行了粒度测试，1000多个表层沉积物进行了重金属含量测试，之后对粒度平均值及 Cu、Pb、Zn、Cr 含量分布进行了分析。结果显示4种重金属含量平面分布特征较为相似，相对高含量分布区主要位于珠江口及其西侧的粤西近海海域，且均呈现由珠江口向西逐渐减少的趋势。以国家标准《海洋沉积物质量》中一类沉积物为参照，Pb、Zn 超标站点范围主要分布在珠江口内及海陵岛西部，Cu、Cr的超标站点范围较广，在调查区域分布广泛。相关性分析显示4种重金属相关性较高，说明具有同源性，由分布图梯度变化可以看出污染物主要来自于珠江口。将该区域重金属含量进行分区分析后认为，在南海北部近岸海域存在4个重金属富集海域，分别位于珠江口海域、上川岛至海陵岛海域、琼州海峡东部及雷州半岛西部。结合粤西沿岸流及琼州海峡西向流等水动力特征对4个区域重金属来源及形成机制进行了分析，得出琼州海峡周边海域沉积物中重金属主要来自珠江径流输入，并认为珠江径流输入的重金属污染物目前最远可到达北部湾东部。最后，为全面了解重金属对该海域生态环境的影响，选用潜在生态危害指数法进行了评价分析，结果显示重度污染区主要分布在珠江口至崖门口，中度污染区在调查区东部至西部均有分布；由珠江口向西至阳江近岸海域存在3个潜在生态危害中度风险区。
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