Acetate-based imidazolium ionic liquids (ILs) are of great importance and widely applied in biomass processing and engineering but under stability issue due to the structure self-rearrangement induced by C-2-H deprotonation, by which the IL based biomass processing will be challenging. Herein, we demonstrated that the thermal stability of normal acetate-based imidazolim [C(8)C(1)Im][OAc] could be significantly improved by changing its cation and anion environment with the presence of 1-butyl-3-methylimidazolium bis(trifluoromethylsullonyl)imide IL ([C(4)C(1)Im][NTf2]. When the molar fraction of [C(8)C(1)Im][OAc] was 0.3, the thermal stability of [C(8)C(1)Im][OAc] could be significantly improved (Delta T-5%dec + 43 degrees C). Detailed information obtained from thermal gravimetric analysis (TGA) and nuclear magnetic resonance (NMR) revealed that the addition of [C(4)C(1)Im][NTf2] played a significant role in enhancing the thermal stability of [C(8)C(1)Im][OAc]. It was proposed that the formation of an anion-pi(+) structure network between[C(8)C(1)Im][OAc] and [C(4)C(1)Im][NTf2]via strong hydrogen bond interactions greatly affects the environment of hydrogen atom in the imidazolium ring of each IL (C) 2020 The Chemical Industry and Engineering Society of China, and Chemical Industry Press Co., Ltd. All rights reserved.