In this study, the interaction between cellulose diacetate (CDA)and ionic liquid(IL) was studied at room temperature (25 ℃) and in the temperature range from 35 to 210 ℃ with 1-butyl-3-methylimidazolium hexafluorophosphate (BMIMPF6) as plasticizer, using Fourier transform infrared spectroscopy (FTIR) and two-dimensional correlation spectroscopy analyzer, guiding for melt process of plasticized CDA in theory. The results showed that at 25 ℃ changes occurred in the positions or intensity of absorption bands assigned to hydroxyl forming hydrogen bonds, acetyl groups in CDA, the anion in BMIMPF6 and C-H in imidazole ring in plasticized CDA compared with CDA, in which absorption peaks’positions would shift or their intensity would become weaker, and the changes depended on the content of BMIMPF6 in CDA. It has proved that there were interactions between BMIMPF6 and CDA, and the interactions were formed between C-H in imidazole ring of BMIMPF6 and acetyl group in CDA, C-H in imidazole ring and C-O in the backbone of CDA, the anion of BMIMPF6 and acetyl group in CDA, which helped destroy and weaken the original hydrogen bonds network structure in CDA. In un-plasticized CDA, the absorption peaks of OH group forming intramolecular hydrogen bonds existing in the whole heating process from 35 to 210 ℃ became gradually weaker and shifted towards the shorter wavelength side with the rise of temperature, and acetyl group absorption bands remained almost unchanged. However the changes of absorption peaks assigned to OH group in plasticized CDA had been accelerated, and the OH group absorption peaks vanished completely at a temperature above 180 ℃. Besides, the absorption bands assigned to CO and C-O in acetyl group and C-O in the backbone of CDA had shifted and decreased in the intensity in plasticized CDA. It can be concluded that the thermal stability of CDA was reduced by BMIMPF6. Then a further investigation into plasticized CDA was carried on in the temperature range from 35 to 170 ℃ by two-dimensional correlation spectroscopy, and the sequential order of the responses from different chemical groups in plasticized CDA towards the variation of temperature was illuminated. The results showed that the dominating changes of interactions in plasticized CDA during heating would start with the interaction between C-H in imidazole ring of BMIMPF6 and CO in acetyl group in CDA, then remove the interaction between anions and cations in BMIMPF6. Subsequently isolated CO, C-O and methyl groups were released fromassociated acetyl groups originally forming H-bonds as H-bonds were broken by heating, and then interacted with anions and cations in BMIMPF6 respectively, which was followed by the interactions between C-O in the backbone of CDA and BMIMPF6. The interaction between CDA and BMIMPF6 was stronger than original H-bonds interactions in CDA and interactions between anions and cations in BMIMPF6, and would be reinforced with the rise of temperature.