Composite cation exchange membranes (C-CEMs) based on mainchain sulfonated polyether sulfone (SPES) and polyvinyl pyrrolidone (PVP) have been prepared and the effects of hydrophilicity on C-CEM properties investigated in a previous work. In this study, membrane properties were optimized by investigating the effects of degrees of sulfonation (DS) on CEM properties. SPES with different DS were synthesized and C-CEMs based on PVP and SPES with different DS easily prepared. SPES structures were characterized by FTIR and the DS tested by acid-base titration. TGA, XRD, AFM, and SEM were used to characterize membrane properties and the results showed that C-CEM hydrophilicity increased with increased DS and the ionic conductivity increased accordingly. The ionic conductivity of S-25/P membrane was 0.098 S/cm and higher than the ionic conductivity of commercial TingRun membrane, at 0.082 S/cm. The feasibility for actual electrodialysis (ED) applications was also explored. ED experiments showed that S-20/P membranes possessed better desalination effects than those of TingRun membranes. Increased DS contributed to the formation of higher densities of ionic clusters and the availability of more ion transport channels. Synergistic effects between ionic clusters and hydrophilicity for ion transport were more significant with increased DS. This study demonstrated that C-CEMs based on mainchain SPES and PVP were optimized by properly improving the DS.