The invention discloses a disperse reactive dye one-bath two-step dip dyeing method for polyester cotton fabric. The method comprises the following steps: S1, pretreatment: padding a polyester cotton fabric to be dyed in a finishing liquid, conducting two dipping and two rolling, pre-drying at 60-80 DEG C, baking at 120-140 DEG C, washing with cold water and drying; S2, polyester dyeing: immersing the polyester in a disperse dye, insulating at 65-75 C, and insulating at 110-130 DEG C; S3, cotton dyeing: adding a quaternary ammonium salt cationic etherifying agent, stirring for reaction, adding a reactive dye, insulating at 70-80 DEG C, adding a dyeing auxiliary, insulating, adding soda ash, and insulating at 60-100 DEG C; and S4, posttreatment: conducting an initial washing, soaping and post washing. The disperse reactive dye one-bath two-step dip dyeing method for polyester cotton fabric has the advantages of simple process, easy industrial implementation, wide dye application, uniform coloration, high fixation rate and good levelness.