Abstract: In order to consummate the dyeing and finishing theory of PTT fiber,ensure the dyeing quality of PTT fabrics,this paper has investigated optima dyeing process and dyeing mechanism of disperse dyes to PTT and PET fabrics through dyeing them with two different types of disperse dyes and measuring the dye-uptake,(K/S) value and colorfastness,and discussed the difference of dyeing behaviour for PTT and PET polyester fibers.The result has showed that the dyeing behaviour of PTT fiber is better than that of PET.PTT fiber is a polyester fiber with excellent dyeability.The optimal dyeing temperature varies with disperse dyes used for dyeing PTT fibers;The two-tone effects of PTT and PET fibers will be obtained in one bath dyeing at 100-(110 ℃),and the union-colour effects of PTT and PET fibers will be obtained in one bath dyeing at 120-(130 ℃).