The invention relates to a shape self-adaptive in-mold decorating method, which comprises the following production steps: 1, conveying a decorating film by a material conveyer; 2, cutting the decorating film; 3, rotating a base plate of a conveyer, and placing the cut decorating film in a vertical position; 4, using a mechanical hand for conveying the decorating film to a position in front of a forming cavity of a mold; 5, using a controllable air flow for regulating the position and the shape of the decorating film; 6, using a material pressing frame for fixing the decorating film; 7, heating the film; 8, carrying out vacuum injection suction forming on the decorating film after the mold assembly, and prefabricating injection molding holes; and 9, controlling an injection molding machine and peripheral equipment to start injection molding, if required after the third step, rotating the cut decorating film for 90 degrees for changing the printing direction of patterns of the decorating film. The decorating film comprises a transfer printing film and an in-mold transfer printing film. The invention has the advantages that the film does not need to be preprocessed and pretreated in advance, products or parts with surface decoration in any shape can be produced only through one work procedure, the production cost is low, and the popularization is easy.