In this work, amorphous Tb20Fe24Co56 (TFC) films are deposited on a polyimide plate by sputtering to investigate the magnetostriction and volume magnetostriction. Also, the effect of the working pressure of Ar gas on the residual internal stress of the TFC film is investigated. It indicates that the residual internal stress of the TFC film ranges from -300 to -121 MPa between 0.7 and 8 Pa of Ar gas pressure. A bilayer cantilever structure is used to evaluate the magnetostriction performance, which indicates that the largest magnetostriction coefficient and volume magnetostriction of the TFC films are 54 and 48 ppm at an external magnetic field of 7490 Oe, respectively. The value of the Joule magnetostriction of the TFC film is almost as same as the volume magnetostriction, which shows that the volume magnetostriction is the dominant mechanism of the magnetic field-induced strain. The homogeneous distribution of elements in the amorphous TFC films possibly makes the Joule magnetostriction small. In contrast with the Joule magnetostriction, the volume magnetostriction is independent of the motion of magnetic domains governed by the magneto-volume effect. Thus, the volume magnetostriction dominates the magnetostriction performance.