Abstract: Objective:To initially observe the cellular irradiated injury by high dose per fraction. Methods:We cultivated human pancreatic carcinoma MIA PaCa-2 cells and and divided them into 0, 2, 5, 10, and 17Gy groups. Cultivated cells were radiated by 6MV-X ray in one fraction with medical processing accelerator. We observed cellular morphous by histo-logical technology after 24hours. The degree of injury of DNA detected by comet assay instantly after radiation and by DNA ladder test at 6 and 12hours after radiation. Changes in cell cycle were explored by flow cytometry at 0, 6, 12, 24, and 36hours after radiation. Results:After X-ray radiation, human pancreatic carcinoma cell line (MIA PaCa- 2) were swell -ing. With the increase of radiation dose (less than 10Gy), apoptotic necrosis and G2/M blockage of cell cycle was more ob -vious. When radiation dose was more than 10Gy, the peak of apoptotic necrosis appeared early and obvious. The degree of DNA injury was most obvious when radiation dose was 10Gyand was decreased when radiation dose was17Gy. When radiation dose was less than 10Gy, DNA ladder was single electrophoresis band. When radiation dose was10Gy group, DNA ladder detection showed multiple typical ladder band. When radiation dose was more than 10Gy, vague irregular bands were observed. Conclusion:Different from conventional dose-fraction radiation, high dose per fraction causes oncot -ic necrosis as the main cell death type.