The invention discloses a method for preparing a polyaniline material with a three-dimensional graded micro-nano structure, and belongs to the field of preparation of high polymer materials. The preparation method comprises the following steps: respectively dissolving an aniline monomer and an oxidizing agent in a strong acid solution, freezing the aniline monomer or oxidizing agent solution into ice, pouring the pre-cooled oxidizing agent or aniline monomer solution onto an ice layer, freezing the materials into ice, finally transferring the frozen ice blocks into a low-temperature environment to carry out polymerization reaction, and obtaining the three-dimensional hierarchical polyaniline materials with different morphologies. According to the method, soft and hard templates are not needed, an organic solvent is not needed, and the reaction time is shorter. The polymerization reaction is carried out in a strong acid environment, the conductive characteristic of polyaniline is ensured, and the hierarchical structure can be regulated and controlled by changing the adding sequence of reactants and the size of an ice layer or adopting a multi-layer freezing mode. The method is simple and controllable in preparation process, high in sample purity, unique in morphology and suitable for large-scale preparation, and has wide application potential in the fields of energy storage materials, adsorption materials, sensing materials, electromagnetic shielding materials, conductive functional materials and the like.