The dyeable modification method of cationic dyes is to copolymerize a polyester dyeing modifier, such as sodium dimethyl phthalate -5- sulfonate (commonly known as trimer, abbreviated as SIPM), with polyester. After copolymerization, sulfonic acid groups are introduced into the molecular chain of polyester, which can be dyed with cationic dyes. The dyed fabrics are bright in color, with high dye exhaustion rate, which greatly reduces the discharge of printing and dyeing wastewater. Copolymerized polyester chips can also improve the antistatic, pilling resistance and moisture absorption properties of polyester, which is an improvement in recent years.