Resource reuse of waste-activated sludge (WAS) from a municipal wastewater treatment plant (WWTP) was introduced as raw material of microbial flocculant (MBF) preparation. With WAS samples of three concentrations, MBF preparation by various methods – including cation exchange resin (CER), CER-ultrasonication, CER-ultrasonication-CER, ultrasonication, ultrasonication-CER, and ultrasonication-CER-ultrasonication methods – were comparatively investigated. According to the results of chemical compositions, concentrations, and flocculating activities of the prepared MBFs, the compound methods excelled the sole methods, and the CER-ultrasonication method was the best. Major compositions of the prepared MBFs contained polysaccharides, proteins, and nucleic acids. Improving sludge concentration was beneficial to extract MBF in high concentrations using the above methods. Appropriate MBF mass dosage was crucial its flocculating activity because less or more dosage would deteriorate the flocculation. The mechanism analysis indicated that CER treatment could provide a good pretreatment for ultrasonication, but became useless when it was set after ultrasonication.