Abstract: A light inducible RNAi system was built by using the light inducible gene expression system. The transfection mass ratio, the expression level of transcription factors and the core promoter of shRNAmir expression vector were optimized. We constructed transcription factor GAVPO expression vectors containing different promoter segments and the shRNAmir expression vectors with different core promoters, and assayed their effects on inhibition of gene expression. The results show that the GAVPO expression level plays an important role in gene silencing and background expression level of shRNAmir. Low expression level of GAVPO can tightly control expression of reporter gene, and reporter gene expression level decreased to about 60%; overexpression of GAVPO can efficiently inhibit the reporter gene expression, and reporter gene expression level decreased to 34%.