There has been a great interest in the strained Si CMOS technology lately, especially the modification of band structures which provides a theoretical basis for the design of the high-speed and high-performance devices and circuits. Calculations were performed on the band structures in strained Si/(111)Si1-xGex(0≤x≤0.4) by the first-principle pseudopotential approach of the plane wave based upon the density functional theory. It was found that the conduction band (CB) edge is characterized by the six valleys all the same, that valence band (VB) edge degeneracies are partially removed and that the electron mass in CB is unaltered under strain while the hole mass decreases along the ［100］ direction with increasing x. In addition, the fitted dependence of bandgap on x are in good agreement with KP theoretical calculation, from which the quantitative data supply valuable references to the devices design.