In this work, imidazolium 2,4,5-trinitroimidazolate was obtained from 2,4,5-tri-iodoimidazole in a yield of 48%. Single-crystal X-ray diffraction analysis showed that this compound belongs to the triclinic crystal system with space group P-1. Thermogravimetric-differential scanning calorimetry (TG-DSC) was performed under a nitrogen atmosphere at heating rates of 5, 10, 15 and 20 °C·min−1. Compound 3 clearly exhibits an exothermic decomposition. The activation energy (E) and pre-exponential factor (lnA) calculated by the Kissinger method were 113.67 kJ·mol−1 and 25.30 s−1, respectively. The E values obtained by the FWO and KAS methods changed slightly from 103.33 to 113.69 kJ·mol−1 and from 101.52 to 111.97 kJ·mol−1, respectively, which makes us believe that its thermal decomposition can be described using only one reaction model. The Šatava-Šesták method and the compensation effect were used to study the thermal decomposition mechanism of imidazolium 2,4,5-trinitroimidazolate. [Formula] is regarded as the most appropriate thermal decomposition kinetic equation. The impact sensitivity, friction sensitivity, detonation velocity and explosion pressure of imidazolium 2,4,5-trinitroimidazolate were 43 cm, 46%, 7056.9 m·s−1 and 1.9703 · 1010 Pa (ρ = 1.538 g·cm−3), respectively. Imidazolium 2,4,5-trinitroimidazolate is incompatible with RDX, HMX, TKX-50 and CL-20.