The invention provides a WSiAlN thin film for a piezoelectric thin film transducer and a preparation method thereof. The WSiAlN thin film for the piezoelectric thin film transducer comprises a bottom electrode and a piezoelectric thin film located on the bottom electrode, wherein the bottom electrode is made of a material WSi, and the piezoelectric thin film is made of a material AlN. According to the invention, the bottom electrode is made by adopting the material WSi and arranged below the AlN piezoelectric thin film, so that the c-axis orientation of the piezoelectric thin film can be improved, the stress is reduced, and requirements of a composite thin film material for the piezoelectric thin film transducer are met. The composite thin film material structural unit provided by the invention, namely, the WSiAlN thin film, can act as a novel thin film material structural unit to use in the piezoelectric thin film transducer.