RNA interference is a newly emerging gene block technology. Exogenous and endogenous double stranded RNA in cells can restrain specific sequence gene expression. RNA interference can block the specific gene expression efficiently, and identify the upper or lower reaches of the relationship of the different genes in the complex signaling pathway. It is a powerful tool to study signal transduction pathway. RNA interference can inhibit targeted gene expression of mRNA and protein products. It could simply, specifically, efficiently and stably reduce targeted gene expression, and it could remove the target gene without affecting other materials. RNAi technology is better than any previous methods in gene function's study and application. But, it is hard to transfect the RNA into mammalian cell lines, and mammalian cells also generate antagonism to the double stranded RNA or small interfering RNA. Thus, we are looking forward that using highly effective and safety small interfering RNA in medical care.