Abstract: To solve low efficiency in enhanced extraction of medium-deep low-permeability coal seam gas and address nanofluid aggregation and instability in complex coal pores, non-toxic, eco-friendly, low-cost fatty alcohol polyoxyethylene ether sodium sulfate (AES) anionic surfactant was used to modify SiO₂ nanoparticles and prepare an AES-SiO₂ active nanofluid system. High-rank anthracite (SX) from Jincheng, Shanxi was adopted to systematically study macroscopic mechanisms of nanofluid modification, coal wettability and CH₄ displacement via Zeta potential, surface tension, contact angle and gas displacement tests. Molecular dynamics (MD) combined with Grand Canonical Monte Carlo (GCMC) simulations revealed microdynamic processes of coal wetting improvement and CH₄ effective displacement by active nanofluid. Results show AES molecules adsorb on coal matrix surfaces through hydrophobic chains. Their polyoxyethylene ether sulfate groups produce steric hindrance and hydrophilic effects, and form physical composites with SiO₂ nanoparticles by electrostatic adsorption. This synergistically suppresses particle agglomeration and improves dispersion stability. At 0.1% nanofluid concentration, absolute Zeta potential reaches 60.43 mV, surface tension hits the minimum and dispersion stability peaks. At this concentration, coal contact angle drops to 40°, surface free energy reaches 28 mJ/m², and wetting improvement outperforms pure AES solution or SiO₂ nanofluid. The 0.1% AES-SiO₂ nanofluid yields CH₄ desorption capacity of 8.74 cm³/g and displacement capacity of 4.54 cm³/g, with desorption saturation time shortened to 150 min. The AES-SiO₂ composite increases coal-water interaction energy (−1.29 J/mol), reduces coal-CH₄ interaction energy (0.26 J/mol), and raises H₂O diffusion coefficient (0.74×10⁻⁵ cm²/s) and CH₄ diffusion coefficient (3.03×10⁻⁴ cm²/s). Consequently, the H₂O density peak rises and shifts forward (<4 nm), while the CH₄ density peak falls to 0.10 and shifts backward (>8 nm). This promotes coal hydrophilic transformation and efficient CH₄ displacement. This work provides theoretical support and technical guidance for enhanced gas extraction in low-permeability coal seams.