RNA interference (RNAi) is the process that the introduction of exogenous or endogenous double-stranded RNA (dsRNA) into a cell leads to special degradation of homogenous mRNA and suppression of relative gene expression. Because of being able to highly specially and efficiently silence gene expression, RNAi has the potent application in the study of gene function and regulation, signaling pathway, drug target validation and gene drug development. RNAi possible molecular mechanism, molecular biological characteristics, productive ways and its application in studying tumor are summarized.