In order to study the quality of sediments and seawater in the mangrove area of Xincungang, Hainan province, the particle size, heavy metals, nutrients, organic carbon, sulfide and total salt of sediments, as well as the dissolved oxygen, nitrogen and phosphorus of seawater in this area were analyzed. The potential ecological risk index method, membership fuzzy comprehensive evaluation method and other evaluation methods were used to evaluate the sediments and seawater. The results showed that the content of trace elements in the sediments was relatively low and uniform. The content of total phosphorus in a few points and the content of organic carbon was relatively high, while the content of sulfide was very low, and the area belongs to medium or strong saline soil. The contents of dissolved oxygen, ammonia nitrogen and total phosphorus in seawater had significant differences in some sections, and the contents of total nitrogen, inorganic nitrogen and nitrate had nothing to do with the sections. According to the evaluation results, Heavy metals and nutrients in sediments had no ecological risk effect, Organic carbon, sulfide, petroleum, heavy metals and other indicators meet the quality standard of class I marine sediments, but the characteristics of seawater nitrogen pollution were obvious.