Abstract: The aging of cellulose insulating paper can be accelerated by hexadecanethiol contained in transformer oil. It is valuable to reveal the microscopic mechanism of hexadecanethiol on cellulose aging to optimize sulfide-resistant measures for insulating paper. However, most of the existing studies about the effects of the hexadecanethiol on the aging of insulating paper mainly focus on experimental methods, and the microscopic mechanism is not clear. Therefore, the simulation method of reactive molecular dynamics was used to preliminarily study the microscopic mechanism of hexadecanethiol on the aging of insulating paper. The results show that, with the increase of hexadecanethiol concentration, the number of free radicals produced by the pyrolysis of hexadecanethiol will increase, which are easy to react with cellobiose molecules. These radicals attack cellobiose molecules in four main paths. Through comparative studies, it can be found that the secondary hydroxyls of cellobiose molecules are the main target of free radical because of their low energy required for the reaction. This conclusion preliminarily reveals the microscopic mechanism of hexadecanethiol accelerating the aging of insulating paper at the molecular level, which is expected to provide a certain theoretical basis for the optimization of the sulfide-resistant measures for insulating paper.