The thermal decomposition properties of 5, 5'-bis(2, 4, 6-trinitrophenyl)-2, 2'-bi(1, 3, 4-oxadiazole) (TKX-55) at normal pressure(0.1 MPa)and high pressure (5.0 MPa) were studied by differential scanning calorimetry (DSC) and thermogravimetric analusis (TG).The thermal decomposition kinetic parameters of TKX-55 at normal pressure were calculated by Kissinger's method and Ozawa's method and compared with those of hexanitrostilbene (HNS) to study the correlation between molecular structure and its properties.Results show that compared with normal pressure state, the shape of exothermal peak of thermal decomposition behavior of TKX-55 under high pressure is sharper.Under the high pressure environment (5.0 MPa), TKX-55 still maintains high thermal stability.The initial decomposition temperature is 355.69 ℃, which is about 35 ℃ higher than the initial decomposition temperature of HNS.With increasing the heating rate, the decomposition peak temperature of TKX-55 and HNS is shifted to high temperature, and the decomposition peak temperature of TKX-55 at different heating rates is obviously higher than that of HNS.The decomposition.activation energy of TKX-55 obtained by integral isoconversional non-linear method (NL-INT method) is 233.71 kJ·mol^-1 and the decomposition.activation energy of HNS is 197.87 kJ·mol^-1.The decomposition activation energy of TKX-55 is obviously higher than HNS, indicating that TKX-55 has more excellent thermal stability than HNS.