There has been much interest lately in the strained Si CMOS technology used for carrier mobility enhancement. The dispersion relation of valence band in strained Si is the theoretical basis for understanding and enhancing hole mobility. With in the frame of K.P theory, the dispersion relation is derived by taking strained Hamiltonian perturbation into account. The corresponding model obtained can be applied to calculate the valence band structure and hole effective mass along arbitrarily K wavevector direction in strained Si grown on arbitrarily oriented relaxed Si1－xGex(0≤x≤0.6) substrates, and hence is valuable as reference for the design of devices.