The invention relates to the technical field of 
yarn dyeing and finishing, and particularly discloses a 
polyester-cotton blended 
yarn dyeing process. The 
polyester-cotton blended 
yarn dyeing process comprises the following steps of S1, performing yarn pretreatment; S2, performing washing and 
drying; S3, performing primary dyeing: adding 1.5-3 g / L of a 
disperse dye leveling agent into a primary dyeing 
bathtub, performing heating to 75 DEG C, adding a 
disperse dye, then performing heating to 85 DEG C, sending the washed and dried yarns into primary dyeing liquid for dip dyeing at a bath ratio of1: (9-11), and performing heat preservation dyeing for 45-55min; S4, performing reduction cleaning; S5, performing secondary dyeing, wherein the bath ratio is 1: (9-11), the temperature is increasedto 75-85 DEG C, heat preservation is performed for 18-22 min, then the temperature is increased to 90 DEG C, heat preservation dyeing is performed for 30-35 min, and secondary dyeing liquid is activedyeing liquid; S6, performing soaping; and S7, performing 
dehydration and 
drying, wherein pretreatment liquid comprises the following components in parts by weight: 3-6 parts of 
pectinase, 4-8 parts of alpha-
amylase, 4-7 parts of 
hydrogen peroxide, 0.5-1 part of 
sodium silicate, 1-3 parts of a penetrant, 0.5-1 part of cocamidopropyl hydroxy sulfobetaine and 65-85 parts of deionized water. The method has the advantages of effectively improving the dyeing uniformity of the cotton-
polyester blended yarns and improving the yarn quality.