In order to screen high-producing-citric acid strains, the original strain 4# was irradiated with different doses of heavy ion beams 12C+6. The citric acid content in the fermentation broth was measured by acid-base neu-tralization. The results showed that the positive mutation rate reached the highest value of 21% as the heavy ion 12C+6 irradiation dose was 60 Gy, and the high producing citric acid strain H4002 was obtained after screening. Compared with the original strain, its fermentation content of citric acid was improved by 18%. The results suggest that high-producing-citric acid strain could be obtained after it was irradiated by heavy ion beams and the mutation effect was remarkable.Cited