Display omitted •Unimolecular mechanisms of DMM combustion were studied using DFT and CBS-QB3 methods.•Rate constants of complex (R1–R4) and simple bond fission (R5–R11) were calculated.•Results show comparable rates using TST and the RRKM theories for different reactions.•Pressure and temperature dependence on reaction mechanisms were investigated.•Branching ratio analysis shows domination of P5 with competition from P6/P7 channels. Many recent studies have been considered dimethoxymethane (DMM) as a potent fuel additive which reduces soot production and nitrogen oxides (NOx) emissions of diesel and biodiesel fuel. This study reports thermo-kinetic investigation of DMM pyrolysis in temperature range 300–2000 K using M06-2X and ωB97XD density functional methods and modest cost ab initio/complete basis set-quadratic Becke3 (CBS-QB3) procedure. The energy profile has been constructed using possible unimolecular H-atom transfer reactions (R1–R4) and simple bond fission reactions (R5–R11). Rate constant calculations were conducted at high-pressure (HP) limit and in the fall-off regimes using classical transition state (TST) and the statistical Rice-Ramsperger-Kassel-Marcus (RRKM) theories, respectively. Based on CBS-QB3 energies, branching ratios analysis reveals unimportance of all H-atom transfer reactions at T ≥ 400 K, while the homolytic bond cleavage reaction R5 which produces CH3 and gauche– OCH2OCH3 fragments is considered the main dominated decomposition channel with high competition from R6 (CH3 and trans– CH3OCH2O) and R7 (CH3O and CH2OCH3) channels especially at elevated temperature.