Process of the separation of waste polyester-cotton fiber with dilute hydrochloric acid was studied. Acid mass fraction, reaction time, reaction temperature and solid-liquid ratio were studied on the effect of separation with the method of Orthogonal experiment. The results showed that the priority order of the factors was reaction time > acid mass fraction > reaction temperature > solid-liquid ratio. The optimal conditions through serious research on such factors were: acid mass fraction 10%, solid-liquid ratio 4g/100ml, reaction temperature 95°Cand reaction time 90 minutes. Through the microscope, polyester and cotton fibers were separated completely in which polyester into fibrous and cotton fibers were hydrolyzed into tiny powder.