The invention discloses a scandium-doped aluminum nitride film and a preparation method thereof, and belongs to the field of piezoelectric films. A high-purity scandium aluminum alloy is adopted as a target; a C276 alloy substrate is used as a substrate; nitrogen is injected in a reaction cavity as reaction gas under an inert environment; and an ScAlN film is deposited on the C276 alloy substrate through a magnetron reaction sputtering method. All performances of a piezoelectric film are improved through doping of an Sc element and proper process parameters; the crystal structure of the film is excellent; grains cylindrically grow along a c axis; the piezoelectric constant is the highest to reach 16.5 pC/N; the surface topography of the film is excellent; the propagation loss of surface acoustic waves can be reduced; the film is higher in resistivity and lower in leakage current, so that the insulation performance is excellent; in addition, the dielectric constant of the film is 10.3-13.6 at 1 MHz; and the dielectric constant is increased while no electromechanical coupling coefficients are caused. The prepared piezoelectric film has the application prospect in the field of surface acoustic wave devices and the field of piezoelectric energy collectors.