Objective：To investigate the effects of irinotecan（CPT-11）combined with X-ray treatment on the proliferation and apoptosis of human colon cancer cell line HCT-116. Methods：MTT method was used to detect the effects after treatment with different concentrations of CPT-11（10，20，30，40，50 μg/mL）for 24 hours and single dose of X-ray（3，6，9，12，15 Gy）on the proliferation of HCT-116. The proliferation rates of the three groups of cells were detected by clone formation assay，the apoptosis of the three groups was observed by AO/EB staining，and the levels of p53 and p21 protein were detected by Western blot. Results：CPT-11 inhibited the proliferation of HCT-116 cells in a dose-dependent manner in the range of 10~50 μg/mL. After pretreatment with CPT-11 at 10 μmol/L，combined 3，6，9，12 and 15 Gy X-ray irradiation showed that the inhibition rate of proliferation in the combined treatment group was higher than that in the irradiation group，and the difference was statistically significant（P < 0.05）；compared with the control group and the irradiation group，the combined treatment group had a dose-dependent inhibition effect on the proliferation of HCT-116 cells. The number of colony formation decreased significantly（P < 0.05）；the levels of p21 and p53 in the combined treatment group were significantly higher than those in the other two groups（P < 0.05），and the apoptotic rate also increased significantly（P < 0.05）. Conclusion：Iritican combined with X-ray irradiation inhibits the proliferation and induces apoptosis of human colon cancer cell line HCT-116，which may be related to the activation of p53 and p21.