Abstract: Fluorescence in situ Hybridization(FISH) is a kind of technology of non_radioactive in situ Hybridization, which have developed in 80'S . As a new molecular cytological method, it has widely been used in cellular genetics and molecular biology. This article briefly summarized basic principle and trait of FISH and the application of FISH in botany, including identification of alien chromatin, physical mapping of genes, chromosome RNA and genome evolution.