Flocculation is one of the most important water pollution control methods. Flocculant is a key foundation of flocculation pollution control method, which plays a vital role in the final water treatment effect. Among these, cationic polyacrylamide is an important type of water treatment agent, which has been of concern in the field of water treatment. The initiation system in the free radical copolymerization and research progress of cationic polyacrylamide are summarized. Characteristics and application of initiation system in the polymerization, such as azo-initiator system, redox initiation system, complex initiation system and UV initiation system are introduced mainly. The types and application of common cationic monomers in the copolymerization are elaborated. Furthermore, its future development tendency and research direction are predicted.