A sulfonated chitosan superplasticizer (SCS) was synthesized from chitosan, maleic anhydride, and sodium metabisulfite via amidation and sulfonation. The structure and molar masses were confirmed by FTIR, H-1 NMR, and GPC. The application performance was determined by water-reducing ratio, paste fluidity, setting time, hydration heat time curve, compressive strength, pore structure, and SEM images. The results indicated that SCS has high water-reducing ratio, better paste fluidity, and suitable setting time at low water-to-cement ratio (0.29). The working mechanism of SCS was revealed by the adsorption behavior of SCS and the zeta-potential of cement. The results demonstrated that SCS and polycarboxylate superplasticizers (PCs) have great similarity in molecular structure and performance, and SCS exceeds PCs with regard to retarding effect and improving compressive strength. This study, especially, demonstrates that a high-performance superplasticizer may be synthesized using a renewable natural polymer and simple synthesis methods, which will be a trend for the future.