Abstract: Hydroxyl-terminated polybutadiene/polyether (HT-PB/PE), serving as binders and fuel for rocket propellants, has been widely studied and applied. To meet the developing demand of industrialization, the modification of HT-PB/PE based on their structural and functional characteristics has become one of the hot topics. In this study, the modified HTPB and the modified HTPE were prepared by modification of end groups and main chains. After the preparation, the characteristic functional groups of the binders were characterized by infrared spectroscopy (FTIR) to determine the effective end-group modification. Nuclear magnetic resonance hydrogen spectroscopy (¹H-NMR) was used to characterize the main chain on modified binders through the variation of chemical environment of hydrogen. The analysis of the pyrolysis properties of the modified binders was performed by thermo gravimetric analyzer (TGA). The results effectively reflected the initial and maximum decomposition temperatures, as well as the pyrolysis stage of the above binders. The above characterization results confirmed the effective synthesis of modified binders and their good thermal properties. However, the present reports lacked the studies on the pyrolysis mechanism of these modified binders. To further investigate the effect of end group and main chain modification on the pyrolysis properties of binders, the pyrolysis of modified binders was conducted in a U-shaped fixed-bed reactor, which was connected to photoionization mass spectrometry (SPI-MS). SPI-MS was used to monitor the dynamic evolution of the pyrolysis product as a function of temperature in real-time. The mechanism of the pyrolysis process of the modified binders was studied based on the above tests. The results showed that the end-groups and main-chain modified binders of HTPB exhibited different thermal stabilities. The influence of main chain modification on the pyrolysis behavior was greater than that of end group modification. The pyrolysis mechanism of modified binders followed random bond breaking of C—C and C—O bonds and the increasing varieties of products. The esters and acids were found in the pyrolysis products of the end-group modified binders. The epoxides and alcohols were found in the pyrolysis products of the main-chain modified binder, showing the more pathways during their pyrolysis process.