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(trifluoromethylsulfonyl) imide IL ([C

4

C

1

Im

]

[NTf

2

]

). 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 (Δ

T

5%dec

=+43℃). Detailed information obtained from thermal gravimetric analysis (TGA) and nuclear magnetic resonance (NMR) revealed that the addition of[C

4

C

1

Im

]

[NTf

2

]

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-π

+

structure network between[C

8

C

1

Im

]

[OAc

]

and[C

4

C

1

Im

]

[NTf

2

]

via

strong hydrogen bond interactions greatly affects the environment of hydrogen atom in the imidazolium ring of each IL.