Switchable ionic compounds have wide applications in chemical processes. A switchable ionic compound based on 1,8-diazabicyclo-[5.4.0]-undec-7-ene (DBU), CH3OH and CO2 was synthesized and characterized. DBU/CH3OH/CO2 ionic compound was prepared in the presence of excess methanol, and then the excess methanol was removed by reduced pressure distillation in CO2 atmosphere. The product yield (100%) reached the theoretical maximum for the first time. Its structure was identified by NMR, FT-IR, and XRD. The crystal product shows 8 strong peaks in XRD at 2 theta values of 16.0547 degrees, 16.4308 degrees, 16.7651 degrees, 18.8714 degrees, 19.2140 degrees, 21.9471 degrees, 22.0780 degrees, and 25.5661 degrees. Its decomposition onset temperature (53 degrees C) was affirmed by TGA, which is lower than its melting point. And its ionic switch point was measured by conductivity. (C) 2015 The Chemical Industry and Engineering Society of China, and Chemical Industry Press. All rights reserved.