Abstract: RNA interference (RNAi) has been extensively used for sequence-specific silencing of gene function in C.elegans, Drosophila, mouse and rat. The generation of RNAi transgenic mice made it possible to knock down gene expression at the whole organism level in mammalian species. In this review we described the design strategy of RNAi vectors，compared the difference of gene knock-down from knock-out , and summarized the advantages and unresolved issues concerning RNAi transgenic mice. The contribution of RNAi transgenic mice to functional genomics and of its prospect for application were also discussed.