Abstract: In order to consummate the acid-dyeable polyester(PTT) fibers,realize one-bath dyeing blended fabric,reduce cost,and ensure the dyeing quality of PTT fabrics,a novel polyamide was obtained through polymerization by dimethyl terephthalate(DMT) and triamine used as an additive to improve the acid-dyeable ability of the polyester.The effects of the additive on the mechanical properties and crystallization of the modified PTT fiber were studied. The dyeing test was conducted with acid dyes,at the same time the dyeing mechanism and conditions were also discussed.The results showed that the compatibility of the blends was good,the particles of additive were fully dispersed,the mechanical properties and crystallization of the modified PTT fibers were also good,the maximum dye-uptake of the acid dyeing on PTT fibers was over 65%.