Abstract: Generally;the distribution of the poplars in the world is from temperated zone to middle subtripical zone,their compositions are rather pure and their constructions are rather simple.The appearance of poplar forest in Hainan Island is a new discovery and a new distribtion in the world.This research is a synecology on that poplar association.The Result has been found that it is a multispecies,multi-layers,tropical coniferous and broad-leaved mixed forest which the dominant is poplar,that its species composition is belong to 12 family,13 genus,16 species which most are tropical essen tial,as 13 species are tropical(81%),and that in the forest the relative density,relative dominance,relative frequency and the importance value index of the Populus qiondaoensis sociation are the first,and of the pinus lateri sociation are the second.These two species are the dominant and the snb-dorninant of the association.They are tall and straight.The former is 120cm in b.h.d.and the latter is 38m in height.Their single tree volume can approach about 16-17m3.From the result of this study,it is recommended to research and develope the topical poplar ecosystem.