Abstract: Fig trees are a keystone species in the ecosystem of tropical rainforest in Xishuangbanna.For the species of their flowers,fig trees (Ficus spp.) are dependent upon Hymenoptera of the family Agaonidae (fig wasps).For the propagation and growing of their kind,the fig wasps are dependent upon the gall (ovaries) of the figs,in which their larvae develop.Thus,the complicated symbioses relationship between fig wasps and fig trees have developed.In this paper,the effects of fragmenting of tropical rainforest on the population structure of fig wasps and fig trees,and the population of Agaonidae and Ficus have been described and reported for the first time.As a foundationnal part of the project of biodiversity conservation on fragments of the tropical rainforest in Xishuangbanna,the survey of fig trees and fig wasps on fragments of the tropical rainforest in Menglun has been done in details.As the result:The total number of fig wasps (Agaonidae) collected was 18000 which consisted of 3 genera and 17 species.The species of Agaonidae and Ficus and their populations which had ever lived in the fragmentary tropical rainforest were directly effected,because that the size of fragmented forest is closely interrelated with the number of species which live in it.There are reciprocal and specific relations between figs and fig wasps.