The glycolysis reactions of PET bottle, PET particle and PET fibers were investigated using diethylene glycol (DEG) and SnCl2 as the catalyst in a one-step feed and stepwise feeding process. The structural and thermal properties of the PET materials and their glycolysis products were characterised by SEM, DSC, TG, FTIR, 1HNMR and other analytical means. The results showed that the chemical structures of the three different forms of PET materials were similar with no significant changes. The melting point (253 °C) and crystallinity (43.44%) of the PET fibers were higher than those of the PET bottle and PET particle. When the glycolysis temperature was 220 ℃ and the reaction time was 180 min, the conversion ratio of PET materials by one-step feeding process was: bottle ≈ particle ? fibres (98.8%, 98.8%, 80.8% in order); When the glycolysis temperature was 220 ℃ and the reaction time was 90 min, the conversion ratio of PET bottle and particle by stepwise feeding process reached 100%, and the conversion ratio of fibers reached 92.5%. The conversion ratio of one-step feeding process was 42.1% for bottle, 38.5% for particle and 28.0% for fibers, which increased by 57.9%, 61.5% and 64.5% respectively. The result shows that the stepwise feeding process in this paper can reduce the glycolysis time of PET material by half, and the conversion ratio of PET fibers can be improved significantly.