The relations between the survival and dose of D.radiodurans and E.coli by N~+ ion implantation were investigated. Two curves of survival all take a "saddle shape"with increasing N~+ ion implanted doses
and these are essentially different from the results of UV and γ-ray irradiation. Since the existing theory can not explain this"saddle shape" curve
a possible and reasonable explanation is put forward
based on the energy and momentum deposition effect for lower doses and the charge stimulating effect for higher doses.