[en] pcEgr-TNF plasmid was constructed and transfected mouse NIH3T3 cells to study the level of TNFα expression after different doses of X-ray irradiation. The results demonstrated that the level of TNFα expression of irradiated groups are higher than that of 0 Gy group. The expression of 75 mGy, 5 Gy and 10 Gy group are higher than that of 0 Gy group significantly (P < 0.05-0.001). The results indicate that the recombinate plasmid can be activated by ionizing irradiation and induce expression of downstream gene. Low dose irradiation can induce the expression of downstream gene may be of some potential significance in tumor therapy