Local structure of Cu in a type-I Ba 8 Cu 4 Si 42 clathrate has been investigated by synchrotron X-ray powder diffraction, Cu K-edge extended X-ray absorption fine spectroscopy, X-ray absorption near edge spectroscopy (XANES) and theoretical calculation. It is found that XANES spectra cannot be explained by the substitution of Cu atoms at Si16i, and Si24k positions. Our calculations show that the binding energies of the Si atom in Si16i, Si24k and Si6c positions are 9.000, 9.495 and 8.911eV, respectively. Both experimental and theoretical results support that Cu atoms in the type-I Ba 8 Cu 4 Si 42 clathrate, as a doped element, prefer to occupy the least-binding Si, i.e., the Si6c sites. No structural change between 112 and 300K was observed and the (100)-faceted cubic crystal has negligible distortion/ordering according to transmission electron microscopy.