Abstract: Using cellulose nanofibers (CNF) as a scaffold, CNF/PEDOT:PSS composite products were prepared via in-situ polymerization of 3,4-ethylenedioxythiophene (EDOT), followed by dispersion in deionized water to obtain 3D printing ink. A systematic investigation was conducted on the influence of the CNF-to-PEDOT:PSS mass ratio on the chemical structure, electrochemical properties, rheological characteristics of the ink, 3D printed part quality, and functional application performance of the composite. Results indicate: Increasing CNF content enhances intermolecular hydrogen bonding, crystallinity, and interfacial compatibility, but excessive CNF readily causes agglomeration. CNF content regulates ink viscosity and shear thinning behavior. Low CNF content leads to insufficient ink support and structural collapse during printing, while excessive CNF causes uneven filament extrusion. A CNF:EDOT mass ratio of 2∶5 balances ink processability and printing quality. The optimized ink formulation enables precise printing of conductive circuits (enabling touch-activated illumination of miniature bulbs) and photothermal-responsive snowflake structures (revealing distinct patterns under light exposure), validating the material's conductive and photothermal functionalities. This research provides a practical technical pathway for developing functional 3D-printable materials in flexible electronics and smart decorative applications.