The invention discloses an a-axis oriented reinforced type AlN film and a preparation method thereof, and belongs to the technical field of electronic information functional materials and elements. The preparation method includes the steps that an n-type Si(100) substrate is adopted and put into a magnetron sputtering system cavity to be subjected to vacuumizing treatment, different magnetron sputtering processes and annealing treatment are combined, an a-axis oriented AlN buffering layer is prepared firstly, and the AlN film is grown on the basis of the a-axis oriented AlN buffering layer in a preferred orientation mode; as the lattice matching degree of the AlN film and the AlN buffering layer is high, the growth quality of the AlN film is improved, the surface roughness of the AlN film is lowered, the piezoelectric effect of the AlN film is improved, and transmission loss of acoustic surface waves is lowered. The preparation method is easy to operate and implement in the preparing process, is environmentally friendly and saves energy, the raw materials are in abundant supply and low in price, the batch production process is controllable, batch production, application and popularization are facilitated, and the a-axis oriented reinforced type AlN film is suitable for manufacturing high-performance communication elements in the modern communication technology.