In order to investigate the thermal decomposition mechanism of the energetic cocrystal TKX-55 and the effect of solvent component dioxane （1，4-dioxane， DIO） on the decay of the energetic component 5，5´-bis（2，4，6-trinitrophenyl）-2，2´-bis（1，3，4-oxadiazole） （BTNPBO）， the molecular dynamics simulations on TKX-55 and pure solvent component DIO were carried out with the ReaxFF-lg （Reactive Force Field-Low Gradients） force field. The results show that the initial decomposition reaction of TKX-55 includes the dimerization of energetic molecules， the hydrogen transfer between energetic and solvent components， the ring-opening reaction of 1，3，4-oxadiazole in energetic components， and the dissociation of nitro group. The dimerization reaction facilitates the rapid growth of the subsequent clusters， and the release of the heat and the stable small molecule products are restricted by the formation of a large number of clusters. It is one essential reason for the high heat resistance of TKX-55. For the pure solvent， the heat release and clustering are constrained at low temperatures； while enhanced at elevated temperatures. The main role of DIO molecules in TKX-55 is thought-to adsorb small reactive intermediates （such as OH， NO， NO₂， etc.） and thereby inhibit the decomposition of BTNPBO.