The present study was to explore the influence of up-regulated and down-regulated Cox-2 gene expression on the growth and the radiation sensitivity to transplanted tumor of esophageal cancer EC9706 in nude mice. Constructing siRNA vector for Cox-2 gene and Cox-2 gene eukaryotic expression vector, shifting to esophageal cancer EC9706 cells by the technology of lipofectamine, and obtaining stable transfected cell line by G418 screening. Taqman real-time RT-PCR and Western blot separately detect Cox-2mRNA and Cox-2 protein expression level; the experiment on transplanted tumor in nude mice detects the growth inhibiting role of up-regulated and down-regulated Cox-2 expression combined with X-radiation on esophageal cancer. The sequencing confirms the construction of siRNA vector pRNA-U6.1-siCox214 for Cox-2 gene, the results of RT-PCR and Western blot reflect that Cox-2 gene expression of transfected esophageal cancer EC9706 cells is an efficient silence. The average volume of transplanted tumor for nude mice in Cox-2 down-regulated group is significantly less than that in control group; and while the average volume in Cox-2 up-regulated group is significantly more than that in control group. Down-regulating Cox-2 expression can inhibit the growth of transplanted tumor for human esophageal cancer EC9706 in nude mice, enhance the sensitivity of tumor volume to radiotherapy, and up-regulating Cox-2 expression will make tumor radiation produce the resistance.