Abstract: Neutron radiation effect is one of the important reasons which cause semiconductor devices damage in radiation environment. The Geant4 simulation method of ionizing energy loss (IEL), non-ionizing energy loss (NIEL) and atom vacancies density induced by neutron was introduced in this paper. IEL can be used to analyze total ioniz-ing dose effect, while NIEL can be used to analyze displacement damage. IEL kerma (kinetic energy released in material) factor quantitatively explained the enhanced ioniz-ing effect of CMOS microprocessor induced by neutron radiation. Using atom vacancies density simulation results, additional trap density induced by neutron was calculated, and the enhancement influence on ionizing effect from displacement damage was researched. The experiment and simulation results show that the ionizing energy deposition induced by neutron causes the accelerated degradation of CMOS microprocessor.