The cationic polyacrylamide is synthesized by acrylamide (AM) and propenoyl-ethyl trimethyl ammonium chloride (DAC) through inverse emulsion polymerization, using liquid paraffin as continuous phase and Span80-Tween80 as compound emulsifier. The influence factors for the viscosity of product and the stability of the system are discussed, such as the ratio of oil to water, emulsifier dosage, monomer dosage, cationic degree and initiator dosage. When the volume ratio of oil to water is 1∶1.6, the emulsifier dosage is 30%, the monomer dosage is 30%, the cationic degree is 60%, i.e. the molar ratio of AM to DAC is 2∶3, and the initiator dosage is 0.15%, the obtained product has high viscosity and stability. The effects of viscosity and polymer dosage on flocculating are studied in flocculating experiment, and the polymer structure is analyzed by IR spectrum.