The effects of Al thin film on the properties of ZnO thin film in (002)ZnO/Al/(100)Si composite structure and the optimum thickness of Al thin film when the thickness of ZnO thin film is fixed are discussed by RF magnetron sputtering.The structure of ZnO films is investigated by X-ray diffraction (XRD) spectra.The surface morphology and piezoelectric properties of ZnO films are characterized by scanning electron microscope (SEM).Meanwhile,the ZnO films are analyzed from a perspective of film growth mechanization.The results show that (002)preferred orientation of ZnO thin films in (002)ZnO/Al/(100)Si composite structure and the crystallization property are enhanced obviously compared with the (002)ZnO/Si structure.When the thickness of aluminum is 100nm,the electromechanical coupling coefficient of ZnO thin films in (002)ZnO/Al/(100)Si composite structur e is 65% larger than that in the (002)ZnO/Si structure.The conclusion establish es base for studying the ZnO/Al/diamond/Si composite structure and will be of great importance in developing new high-frequency surface acoustic wave (SAW ) devices.