The invention belongs to the technical field of flocculant preparation, and relates to a preparation method of ternary copolymerized amphoteric polyacrylamide, wherein the preparation method comprisesthe steps: firstly, preparing a novel cationic monomer AHPTAC, mixing and dissolving the monomer with other two monomers of AM and AMPS, deoxidizing, then adding an initiator, heating up, after a reaction is completed, cooling, dropwise adding the obtained water dispersed system into absolute ethyl alcohol, precipitating, washing, filtering and drying, and crushing to obtain a white solid product. The total mass of the three monomers is 20% of the total mass of the system, and the molar ratio of AM to AHPTAC to AMPS is 1 to 3 to (1-4); the initiator is one or two of VA-044 and ammonium persulfate-sodium bisulfite; the adding amount of the initiator is 0.2% of the total mass of the three monomers. The preparation method is simple to operate, and the prepared ternary copolymerized amphoteric polyacrylamide has high molecular weight and excellent performance of controllable cationic degree, and has the advantages of better solubility, wide applicable pH range and better flocculation effect.