The present invention is directed to an aripiprazole oral soluble film and a preparation method thereof. The aripiprazole oral soluble film comprises 10-60% w/w of aripiprazole in a crystalline state and 30-95% w/w of one or more film-forming materials, wherein 90% of the aripiprazole particles have a size of ≤14.3 μm and are uniformly blended in the film without visible undispersed particles. The aripiprazole oral soluble film has excellent bioavailability, uniformity, stability, and palatability. The oral soluble film preparation is prepared by first grinding aripiprazole particles to have desired small particle sizes, then blending the aripiprazole particles with film forming materials in an aqueous solution to a uniform suspension, defoaming the suspension, and coating the suspension on a substrate and drying it to form a film.