A method for fabricating a three-dimensional network structure material comprises steps: mixing ammonium carboxymethyl cellulose with water or with water and a nanomaterial to form a first gel or a second gel; freeze-drying the first gel or the second gel to sublimate the first gel or the second gel and form a first product or a second product; and heating the first product or the second product at a lower temperature to cure the first product or the second product and obtain a first 3D network structure material or a second 3D network structure material. The present invention uses a simple process using water as the solvent, meeting the environment protection demand and having high economical efficiency. The first and second 3D network structure materials fabricated by the present invention absorb water but do not dissolve in water. Thus, the present invention can be applied to many fields.