This paper presents a theoretical determination of valence-band offsets (VBO' s) on (001 ) and (110) interfaces for St/Ge system under different strain conditions, by making use of an average bond energy theory in conjunction with a deformation potential method. The quantitative relationship between the VBO's and the strain condition (characterized by the composition x in substrate Si1-xGex ) is demonstrated. It is shown that the discontinuity be tween the two average valence-band energies is affected little by the strain condition, while,the discontinuity between the two tops of valence-band has a sensitive dependance on the strain condition, and this effect is mainly due to the alteration of the valence-band structure induced by the uniaxial stress. It is found that the VBO value on (110) interface is somewhat smaller than those on (001 ) interface. i. e., there is a weak relevance to the lattice orienta tion. Present results of VBO's are 0. 74 eV for Ge on St(001 ) and 0. 22 eV for St on Ge(001 ), in very good agreement with experimental data:(0. 74 + 0. 13) eV and (0. 17 + 0. 13)eV, respectively.