RNA interference (RNAi) is a recently developed technique for post-transcriptional gene silencing induced by introduction of double-stranded RNA (dsRNA). In the progress of the study on RNA interference mechanisms, it has been widely used in many researching fields.It's not only be a powerful tool in gene functional research, but also provides a new technique for gene therapy. With development of RNAi technology there has been a new approach for gene therapy for cancers. This paper introduces the research progress in the mechanisms and application of RNAi in cancer therapy.