A series of quaternary ammonium-based (QAB) functionalized polyacrylonitrile fibers as superbase catalysts for C-C bond forming reactions in water were prepared. Alkyl with different chain lengths and benzyl were used to tune the hydrophobicity/hydrophilicity and polarity of the inner surface microenvironment of the QAB functionalized fiber catalysts, and the different microenvironment and the active site synergistically promote the completion of the reaction. The mechanism of the influence of different hydrophilic/hydrophobic catalysts on catalytic activity was proposed. The quaternary ammonium-based functionalized fibers with eight carbon alkyl chains (PAN(QAB-8)F) as the optimal catalyst performed excellently in green water solvent with specific advantages of low catalyst dosage, mild conditions, high efficiency, and extensive substrate adaptation. Furthermore, the PAN(QAB-8)F catalyst is very suitable for the continuous flow process, and more than 86% yield was obtained even after the continuous reaction for 160 h; the fiber can be recovered easily and recycled more than 10 times in the continuous-flow system.