The displacement damage due to non-ionizing energy loss (NIEL) is the main reason of photo-electronic device failure in space radiation environment. The basic mechanisms of NIEL are Coulomb and nuclear interactions of silicon atoms with incident protons at energies ranging from threshold to 1 GeV. In the low energy region where the Coulomb interaction is dominant, the NIEL can be calculated by analytical method and TRIM code. MCNPX/HTAPE3X is used to calculate NIEL when the nuclear elastic and non-elastic interactions between proton and target atoms are significant in the high energy range. The results show that it is reasonable to use MCNPX/HTAPE3X to evaluate the NIEL by recoiling nucleus caused by high energy protons. The combination of analytical method and TRIM code can calculate NIEL induced by Coulomb interaction in low energy range, which gives the NIEL of proton in silicon in an energy range from 300 eV to 1 GeV.