The heavy ions with high linear energy transfer and high relative biological effectiveness are much more deleterious on the male germ cells, ones of the most radiosensitive cells of the body, than low-LET ionizing radiation such as X-ray or gamma-ray. The effects of low-dose heavy ion irradiation on male germ cell adaptation and genetics and the possible mechanism of this adaptation are summarized in our laboratory. Our results showed that the heavy ion irradiation significantly increased the frequencies of chromosomal aberrations in spermatogonia and spermatocytes of mice, the low dose heavy ion irradiation could induce significant adaptative response on mouse testes and human sperm, and pre-exposure of mouse testes with low-dose heavy ion can markedly alleviate damage effects induced by subsequent high-dose irradiation. The increase of SOD activity and decrease of lipid peroxidation levels induced by low-dose ionizing radiation may be involved in this adaptative response mechanism. These studies may provide useful theoretical and clinical bases for radioprotection of reproductive potential and assessment of genetic risks for human exposed to heavy ions in radiotherapy and in outer space environment.