1,3,5-trichloro-2,4,6-trinitrobenzene (TCTNB) is the main byproduct of synthesizing an insensitive explosive 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) and requires environmental management and safe handling during disposal. This study introduces a lime neutralization method for treating TCTNB-containing spent sulfuric acid and systematically investigates the underlying hydrolysis mechanism using mass spectroscopy, Fourier transform infrared spectroscopy (FTIR) and Density functional theory (DFT) calculations. Our results demonstrated that TCTNB hydrolysis was significantly accelerated by increasing the pH from 10 to 12 and the temperature from 22 to 95 °C. The hydrolysis reactions proceeded via nucleophilic aromatic substitution, with preference for targeting the chlorine (Cl) groups of TCTNB over the nitro (NO