Abstract: Based on comparison of data of ferns obtained separately in 1959 and 1997 from the fragment tropical rainforest on the holy hill of Manyangguang in Jinghong County in Xishuangbanna, the changing of fern diversity was studied.Through the time between the year 1959 and 1997, the numbers of fern family, genus and species in the fragment forest have not showed conspicuous change, but their composition (floristic elements) have changed a lot.Among 35 species, 25 genera and 17 family record in the year 1959, 14 species, 5 genera and 2 families have not be seen in the investigation in 1997. They are conjectured having disappeared.Among 38 species, 25 genera and 16 families of ferns recorded in 1997, 17 species, 5 genera and 1 family were new in the fragment forest and they are conjectured appearing after 1959.The disappeared species were mainly, shade tolerant species, while the new increasing ones were mainly heliophyte.In population composition, heliophytes increased and shade tolerant decreased with forest fragmentation.