The general properties of natural space radiation environment are summarized, the basic mechanisms of radiation effects are analyzed briefly, In the Monte Carlo Simulation of the radiation effects, the amorphous target material is assumed, the elastic energy loss of incident particle is calculated by binary collision approximation. The inelastic energy loss of project particle for the high energy is calculated by Bethe-Bloch formulation, Lindhard-Scharff formulation is used for low energy and the interpolation formulation was used for the gap between the high and low energy region. The Kinchin-Pease model is used to calculate the secondary damage caused by the displaced lattice atom. Finally the computed results of 100keV Boron incident on silicon are presented and analyzed.