According to monitoring data of coral reefs from 2007 to 2016,there are 11 families and 113 species of hermatypic corals in Yongxing Islands and Qilianyu Islands,in which Pocillopora damicornis,P.verrucosa, Acropora humilis,Porites lutea,Galaxea fascicularis,Goniastrea pectinata and Cyphastrea serailia were common species.In nearly a decade(2007-2016),species number of hermatypic corals significantly declined in survey area,and 53.85%reduction in species number from 39 to 19 was recorded in Yongxing Island,26.09%reduction from 23 to 17 in Bei Island,73.91%reduction from 46 to 12 in Zhaoshu Island,and 70.59%reduction from 51 to 19 in Xishazhou Island.Analysis showed that the crusting hermatypic corals were stable in species number in nearly a decade,but other type of hermatypic corals showed a sharp decrease,59.26%for branching corals,75.0%for those with thin plate,87.50%for free-living Fungiidae corals and 57.14%for massive corals.The coral ecosystem in the Xisha Sea was gradually affected by anthropogenic activities,outbreak of crown-of-thorns starfish,coral disease, typhoons and global warming,based on the analysis of the changes of coral species composition and community forms in the study area.