The modified resin is used as a multifunctional biological carrier to treat phenolic wastewater (PW) in an anaerobic fluidized bed microbial fuel cell (AFB‐MFC). First, the modified resin was prepared, and the conductive polyaniline (PANI) was polymerized in situ on the surface and pores of the macroporous adsorption resin (MAR) to prepare the modified resin composite material (MAR/PANI). A series of modified resins with different mass ratios of resin and aniline were prepared. The modified resins were characterized by Fourier‐transform infrared spectroscopy, scanning electron microscopy (SEM), specific surface area, and pore structure analysis. Materials Studio (MS) software was used to study the internal interaction forces of PANI and MAR, and the molecular dynamics simulation method was used to analyze and calculate the cohesive energy density. The simulation results are qualitatively consistent with the experimental data. The sorption module in the MS software was used to study the adsorption behaviour of the modified resin to the organic components in the wastewater, and the adsorption mechanism was explained on the atomic scale. When the modified resin with m (MAR):m(An) = 1:0.6 was used in the AFB‐MFC, the chemical oxygen demand removal efficiency of wastewater was increased by 26.2%–88.90%, the voltage was increased by 98.46%–489.2 mV, and power density was increased by 303.28%–131.43 ± 0.17 mW/m2.