Sludge dewatering is an important step for wastewater treatment. Composite degradable flocculant (CDF) was prepared by cationic polyacrylamide grafting onto modified starch with a novel initiator, and characterized by Fourier-transform infrared spectroscopy. Microstructure of flocculated sludge was characterized by Scanning electron microscope (SEM). The study investigated the properties of CDF with the contrast of polyacrylamide (PAM), which showed that the prepared CDF exhibited a highly effective flocculation on sludge dewatering, a higher transmittance and COD removal rate, and a lower value of effluent ammonia nitrogen and total phosphorous. Besides, the fermentation process was analyzed by testing the performance of dewatered sludge (Temperature, pH, ammonia nitrogen, E4/E6 (humic acid absorbance at 465 nm (E4) and 665 nm (E6))). The dehydrated sludge with CDF could be easily compressed into cakes by belt-filter for easy transportation and storage. With continuous addition of CDF and PAM, the corresponding index of capillary absorption time (CST) both increased. Moreover, the total value of CST with CDF was low, showing a good dewaterability. In addition, the sludge index of pumping time and moisture content with CDF were low in contrast with PAM. Fermentation experiments demonstrated that sludge with CDF had a comparatively high temperature and low value of E4/E6. Such novel CDF shows enormous potential in wastewater treatment and sludge fermentation.