Abstract: Objective The small interfering RNA (siRNA) technology is used to silence the expression of COX-2 gene in human glioma cells in vitro, to explore its influence on radiosensitivity in order to provide new ideas and methods for the treatment of glioma. Methods Glioma U251 cells were cultured in vitro and siRNA-based COX-2 gene silencing model was constructed. The expression of COX-2 protein in transfected cells was detected by Western blot, and the optimal sequence was screened out. The experiment was divided into control group and transfection group. Four dose groups of 2, 4, 6, and 8 Gy were respectively irradiated with X-rays, and the experiment was repeated three times. The inhibition of cell proliferation after irradiation was detected by MTT assay and plate colony formation assay was used to detect cells. Survival fractions (SF) and sensitization ratio (SER) were calculated by clicking on a multi-target fit curve, and apoptosis was measured by flow cytometry. Results The expression of COX-2 protein in the transfection group was lower than that in the control group, and the siRNA600 sequence was the most obvious, the difference was statistically significant (P<0.05). The subsequent experiments were all transfected with the siRNA600 sequence. The inhibition rate of cell proliferation in the transfected group was (84.87±3.50)%, (63.62±035)%, (55.05±4.87)%, and (36.85±3.00)%, respectively. The proliferation inhibition effect of the transfected group was significantly higher than that of the control group. The radiation dose increased and the difference was statistically significant (P<0.05). The SF of the transfected group was lower than that of the control group, and the D0 of the transfection group was 4.110, Dq was 1.387, which was lower than that of the control group; in the control group, D0 was 6.908, the Dq was 2.772, and the radio sensitivity ratio SER was 1.680, with significant difference (P<0.05). After irradiation, the apoptosis rate of the transfected group was (3.63±0.45)%, (6.08±0.87)%, (47.97±2.13%), (59.56±3.07)%, respectively, which were all higher than those of the control group, and increased more obviously after 6 Gy and 8 Gy irradiation. Conclusion The silencing of COX-2 gene expression in human U251 glioma cell line U251 by siRNA can improve the radio sensitivity of cells, increase the apoptosis rate and proliferation inhibition of cells after radiotherapy, and reduce the clonogenic rate.