<p>Highly nitrated energetic materials exhibit excellent detonation performance but often suffer from high sensitivity. Regioisomerization is a widely used strategy to regulate their stability. In this study, density functional theory (DFT) calculations at the M06-2X/6-311G(d,p) and M06-2X/def2-TZVP levels were performed to investigate the effect of regioisomerism on the thermal decomposition behavior of three highly nitrated pyrazole-based energetic materials: 5-methyl-3,4-dinitro-1-(trinitromethyl)-1<i>H</i>-pyrazole (<b>1</b>), 4-methyl-3,5-dinitro-1-(trinitromethyl)-1<i>H</i>-pyrazole (<b>2</b>), and 3,5-bis-(dinitromethyl)-4-nitro-1<i>H</i>-pyrazole (<b>3</b>). The initial decomposition pathways were explored, with transition states validated via intrinsic reaction coordinate (IRC) calculations, and Gibbs free energy and wavefunction analyses conducted using Shermo and Multiwfn. The results show that nitro dissociation and hydrogen transfer are the dominant decomposition pathways for compounds <b>1</b> and <b>2</b>, respectively, consistent with their decomposition temperatures. For compound <b>3</b>, which decomposes in hydrated crystalline form, an implicit water model was used to simulate the solvent effect. Although not associated with the lowest energy barrier, the hydrogen transfer to a neighboring nitrogen atom features a relatively favorable barrier (41.1&#xa0;kcal/mol) and substantial exothermicity, making it the most likely initial decomposition pathway for compound <b>3</b> and consistent with its observed low thermal stability. Frontier orbital analysis indicated stable LUMO distributions and moderate Δ<i>E</i> changes for compounds <b>1</b> and <b>2</b> during isomerization. These findings provide insight into how regioisomerism and solvent effects influence the thermal stability of energetic materials.</p>