The epitaxial films of semiconductor optoelectronics Mg2Si are prepared on Si (111) substrates by radio frequency magnetron sputtering. The crystal structures and the micro topography of Mg2Si films are characterized by X ray diffraction and field emission scanning electron microscope. The effects of sputtering power on preferred orientation of Mg2Si films on Si(111) substrates are obtained. The results show that the Mg2Si films with one preferential growth Mg2Si(220) increases firstly with increasing sputtering power from 60 W to 90 W, then decreases after reaching a maximum and the sputtering power is 70 W.