Abstract: To study the inhibitory effect of exogenous dsRNA-mediated RNAi on tobacco CMV (cucumber mosaic virus) infection, the MP gene encoding movement protein which is closely related to virus movement in the host, was selected as the target gene. By cloning the CMV MP gene, combining with sequence analysis and dsRNA evaluation, a 490 bp dsRNA fragment targeted to MP gene was designed and prepared by in vitro synthesis. After co-inoculation with CMV, the RNAi effect of MP dsRNA was comprehensively evaluated with the expression level of MP gene and the symptoms of virus. It was found that exogenous MP dsRNA applied to tobacco leaves could significantly reduce the expression level of CMV in infected plants, and effectively alleviate the infection and damage of CMV. Therefore, exogenous MP dsRNA can be considered for its potential in biological control of CMV in tobacco.