In this paper, a novel inorganic polymer coagulant was prepared by fly ash extract. The technology of preparing the poly-silicic-ferric coagulant by using fly ash extract and potassium ferrate has been designed. The influences of alkali concentration, temperature and heating time on the amount of silicon dissolution from fly ash were investigated. When temperature is 60°C, concentration of NaOH is 1.8mol / L and heating time responses to 38 hours, the content of silicon in the fly ash extract is better than that of the others. The effects of pH and Si/FeO42- mole ratio on morphology of the prepared coagulant were investigated by transmission electron microscopy (TEM). The results indicate that poly-silicic-ferric coagulant can be obtained when regulation of filtrate to pH about 1.4 with dilute sulfuric acid and Si/FeO42- mole ratio is about 3.5. At the same time, through the flocculation experiments of using the poly-silicic-ferric synthesized disposing of the model bentonite suspension, turbidity removal has been up to 90% more in the condition of low dosage.