The electronic structures of nanowire-composite arrays are calculated theoretically in the framework of effective-mass envelope function theory，and various coefficients about electronic transport are obtained. At the same time，a closed-form expression based on boundary scattering theory for lattice thermal conductivity is presented. Then the thermoelectric properties of Si nanowire/Ge host material are investigated as function of the Fermi energy，wire diameter and separation between nanowire sidewalls. The results show that the ZT value of nanowire-composite can be significantly increased by carefully adjusting the correlative parameters of the structure.