Accidents related to pesticides have occurred with increasing frequency in recent years. One such accident, involving O,O–dimethyl phosphoramidothioate (DMPAT), which is an essential pesticide intermediate in the manufacture of organophosphorus pesticides, occurred in Taichung, Taiwan, in 2016. The results of thermogravimetric analyzer, differential scanning calorimetry, and vent sizing package 2 experiments revealed that the atmosphere, heating rate, and stirring conditions of DMPAT affect its thermal stability. Multiple thermokinetic methods were adopted to determine the values of thermal safety parameters. Through multiple linear regression, a reaction model of DMPAT was developed. The time to conversion limit and self-accelerating decomposition temperature were determined. The results of this study provide a reference for ensureing the thermal safety of DMPAT processing, use, storage, and transport and preventing thermal decomposition accidents.