There has been aroused a lot of interest in the strained Si technology in the microelectronic field. Density of states (DOS) is an important physical parameter in strained Si materials. Based on the Kleinerts Variational perturbation (KP) theory related to stress, DOSs of electrons and holes near the bottom of conduction band and the top of valence band are obtained in tetragonal, rhombohedral and monoclinic strained Si grown from (001), (101) and (111) substrates respectively. It is found that their DOSs are obviously different from the ones of cubic unstrained Si, except DOSs of electrons near the bottom of conduction band in rhombohedral and monoclinic strained Si. The quantized model obtained can provide valuable references for understanding the strained Si material physics and developing the theoretical model of the other important physical parameters.