Abstract: Qinglan Mangrove Reserve is located in Wenchang city in northeast Hainan Island,China.To understand species diversity,we investigated all vegetation in this area.A total of 172 vascular plant species were recorded,belonging to 148 genera and 62 families.Among them,24 species were true mangrove species,accounting for 92.31% of mangrove species in the province(26 species),85.71% of mangrove species in whole country(28 species),and 27.91% of mangrove species in the world(86 species).In the survey plots(4040 m²),3670 trees belonging to 29 mangrove species which were more than 1.5 m high were recorded.Among them,Sonneratia caseolaris and Bruguiera sexangula had the highest importance values of 12.90 and 12.33,respectively.In individual quantity,however,Ceriops tagal and Rhizophora stylosa were most dominant.The Qinglan Mangrove Reserve can be divided into one vegetation type group,one vegetation type(Broad-leaved forest),two formation groups(Mangrove and Semi-Mangrove) and twelve formations(Form.Bruguiera sexangula + Xylocarpus granatum,Form.Sonneratia alba+ Lumnitzera racemosa,Form.Rhizophora apiculata + Bruguiera sexangula,Form.Sonneratia caseolaris,Form.Aegiceras corniculatum,Form.Sonneratia alba,Form.Avicennia marina + Sonneratia alba + Ceriops tagal,Form.Rhizophora stylosa + Ceriops tagal,Form.Ceriops tagal,Form.Rhizophora stylosa,Form.Lumnitzera racemosa,Form.Lumnitzera racemosa + Bruguiera sexangula).After 19 years,Form.Bruguiera gymnorrhizaand Form.Nypa fruticans have vanished,the Scyphiphora hydrophyllacea community has fragmented into many small plaques,a new Xylocarpus granatum community has formed,and other communities,like Sonneratia caseolaris have remained stable.