RNA silencing is a high conserved mechanism in organisms that involves sequence-specific RNA degradation. For virus induced gene silencing (VIGS), it is induced by infecting a plant with a plant virus that has had its genome modified to include a sequence identical to that in RNA transcribed from the host gene to be silenced. Up to now, various VIGS vectors based on RNA virus, DNA virus, satellite virus or DNA satellite have been established, these VIGS vectors could suppress gene expression effectively in many important plants including Arabidopsis, tomato and barley. VIGS vectors have been used to study function of genes involved in the signal transduction of N-mediated or Pto-mediated resistance, anti-virus mechanism, and plant development and metabolism. With the determination of complete genome sequences or expressed sequence tags, VIGS has recently emerged as a powerful method for identification of gene functions in plants.