The electronic structure of strained superlattices (SLS) (InAs)n(InP)n(001) are calculated with the Linearized-Muffin-Tin Orbitals (LMTO) band structure method in which the higher energy unoccupied d orbitals are treated by internal summation approach. The effects of In 4d orbitals on band structures are investigated. The valence band offsets (ΔEv) at SLS's are determined by a frozen-potential approach. The results show the bulk-like property is almost recovered in the molecular layers next to the interfaces. The band structure of (InAs)1(InP)1(001) given by the present work is well consistent with those given by more elaborate FLAPW calculation. The ΔEv values determined by the present calculation are in good agreement with those from XPS measurement and FLAPW method in which the core level or the macroscopic average potentials is used as a reference level. The small calculation effort and the satisfactory precision justify the present method as a very effective means for studying the electronic structures of multi-layers SLS.