By using magnetic controlled sputtering of-atoms and evaporating insulator medium, Cu clusters embedded in CdS, a metal-semiconductor film Cu∶CdS has been successfully prepared. TEM is used in studying the microstructure of Cu clusters embedded in the medium CdS. The copper cluster is well embedded in CdS. The size of the triangle-shaped grains, Cu clusters, is from 5nm to 20nm. The Cu cluster and medium CdS are both of polycrystalline structures. And the Cu cluster′s lattice constant expands by about 7%.