RNA interference (RNAi) is applied in the gene therapy of malignant tumors as an effective technique to degrade its homologous mRNA specifically. This technique has been developed quickly in broad prospects. Molecular imaging plays an important role both in gene imaging and in molecular signal transduction. It is used as a direct approach to study the onset and development of disease. The technique of RNAi can be used for preparing molecular probes, for making earlier and specific diagnosis, and for targeted gene therapy of malignant tumors.