In this paper, magnetostrictive film of TbFe x is fabricated by DC magnetron sputtering. Influence of the argon pressure to the film composition is studied both experimentally and theoretically. The results show that the argon pressure can change the composition of the film in relatively large range: When the gas pressure is increased from 0.2 to 0.6Pa, the atomic contents of iron decrease from 69% to 55%. The as-deposited film spontaneous magnetization changes from perpendicular to parallel to the film plane when the iron contents decrease which is indicated by magnetic force microscopy. The studies also suggest that decrease of the plasma temperature and increase of the substrate and target distance can enhance the composition control capability of gas pressure variation.