To address the weak interfacial adhesion between polyphenylene sulfide (PPS) fibers and functional coatings in composite membranes for alkaline water electrolysis, this study employed a sulfonation strategy to modify the surface of PPS fibers. The effects of sulfonation temperature, duration, and acid concentration on the sulfonation degree, hydrophilicity, and mechanical properties of PPS fibers were systematically investigated. The results show that acid concentration is the dominant factor in the sulfonation process; higher concentration of acid can enhance the reaction efficiency and drive the reaction equilibrium forward. Reaction temperature influences the molecular mobility, and elevated temperatures facilitate the process of sulfonation reactions. While prolonged reaction time can promote sulfonation reaction to some extent, excessive duration leads to the degradation of the PPS backbone, significantly reducing mechanical strength of fibers. Sulfonic acid groups were successfully grafted onto the fiber surface, increasing the surface roughness and enhancing the hydrophilicity, with the dynamic water contact angle reduced by approximately 35% compared to untreated fibers. Meanwhile, the treated single fibers retain about 75% of their original tensile strength, satisfying the mechanical requirements for subsequent membrane weaving and coating. In addition, the interfacial shear strength between the coating and PPS substrate is improved from 1.49 MPa to 1.82 MPa.