Abstract: In order to study the effect of nuclear DNA damage induced by different energy and types of particles, a DNA and chromosome atomic model was established and nanodosimetry Monte Carlo code NASIC was developed. NASIC can simulate the interaction process of different kinds of particles in biological media, including physical and chemical process and the biological response. The yields of singlestrand break and double-strand break after the mammalian cell irradiated by sources of ¹³⁷Cs and K shell characteristic X-ray of Al (Al-K) were calculated using NASIC. The DNA atomic model used in this paper is close to the real structure. The calculation results of DNA double-strand break yield are in good agreement with the experiment results.