Molecular dynamics computer simulation has been used to study spectral features of surface OH group of silica. The density of proton vibrational states (PDS) and IR spectrum of the OH group at 80 K exhibit three main peaks at 3810, 780 and 200 cm^-1, corresponding to ν, σ, and γ vibrations of the OH-group. In accordance with experimental data, two bending vibration bands reveal a strong dependence on temperature and the mobility of substrate atoms, unlike the band of stretching vibration. Role of different factors In the mechanism of band shape formation is discussed.