Diamond has the advantages of high thermal conductivity, wide spectral transmission range, large Raman gain coefficient and large Raman frequency shift. Therefore, it has become an important Raman medium to expand the wavelength range and obtain new wavelengths with high power and high beam quality. Based on the first principle, the lattice parameters, band structure, density of states and phonon spectrum of diamond are calculated comprehensively in this work, and the structural characteristics, spectrum, band gap, and electron distribution characteristics of diamond are systematically analyzed. Furthermore, the electron motion state of diamond and the effects of the polarization direction of electric field on the band gap of diamond are analyzed. It is found that the crystal direction of diamond most easily affected by electric field is < 1 0 0 > and the best stability is < 1 1 1>. All intrinsic vibration modes and the corresponding frequencies are obtained, which shows that the Raman gain of diamond is the largest when the pump light is propagated along with the < 1 1 0 > and polarized along the < 1 1 1 >. The multiphonon absorption mechanism in the spectral region is also discussed. The work provides a theoretical basis for the improvement of Raman laser efficiency and wavelength expansion of diamond.