The introduction of copper vacancies in BiCuSeO makes it a promising thermoelectric material in the intermediate temperature range. To clarify mechanisms associated with charge and heat transport in this layered compound, we present calculations of the electronic structures of both the ground and excited states by combining density functional theory (DFT) and X-ray Absorption Near-Edge Spectroscopy (XANES). As copper vacancies are introduced into the structure, the DFT calculations point out dramatic changes to its electronic structure, in agreement with the XANES measurements and theoretical simulations. To understand the enhancement of the transport properties, the charge transfer, the projected density of states and the electronic configurations of the copper-deficient BiCu1-xSeO system have been calculated. The Data point out that Cu vacancies may significantly enhance the charge transfer among the Bi and Se atoms, leaving Cu and O atoms unaffected. The results provide clear evidence for an interlayer charge transfer route involving Bi-Se chains which occur in this layered system.