The invention discloses a side-thickened polyamic acid film, tape casting equipment and a preparation method thereof, and belongs to the field of film preparation. The two lateral side parts of the film gradually increase with the thickness close to the outer edge within an X-wide range, X is 20-200 mm, and the thickness distribution of the film is symmetrical relative to the longitudinal central line of the film. The openness of a lip within a Y length range at the two side parts of a forming mold lip of the tape casting equipment gradually increases with the openness close to the outer edge, and the openness of the lip is symmetrical relative to the longitudinal central line of the lip. The preparation method comprises adjusting the bolt of the forming mold lip to obtain the necessary forming mold lip. According to the invention, since the thicknesses of the two side parts of the film are increased, the strength is increased, the strength of the film at an acting point of a clamping device in a subsequent procedure is increased to avoid unclamping or releasing or edge damage caused by clamping damage and pull damage, so that the product yield is greatly improved; the tape casting equipment and the preparation method disclosed by the invention are easy to achieve, and only the lip bolt is adjusted to increase the openness at the two sides of the lip.