The electronic structures of short period (Si)n/(Ge)m Strainedlayer superlattices (SLS's) are calculated using empirical tight-binding method. The results indicate that due to the zone-folding, only the SLS's with n+m=10 have the posibility to form direct band gap. For SLS's with n+m=10, the type of energy gap is determined by the relative energies of conduction band valleys at Γ, N, and Δ. However, the Ge layers number and the composition of substrate play an important role. For (Si)6/(Ge)4 and (Si)8/(Ge)2 SLS's grown on Si1-xGex substrate, direct or quasidirect band gap could be got for the substrate composition 0.4≤x≤1.0 For (Si)4/(Ge)6, direct gap could be obtained only for 0.3≤x≤0.6, and in (Si)2/(Ge)8 SLS's the gap could not be direct for all substrate composition.