Thermal expansion of TATB-filled polymeric material was investigated by using thermal expansion analyzer. The relationship between thermal expansion of composites and TATB size, as well as dynamical mechanical properties of polymer were studied. It was indicated that the linear coefficient of thermal expansion increased between ambient temperature and 70 ℃ as the size of TATB decreased. There was a corresponding relationship between the changes of thermal expansion properties of TATB-filled composite and the apex of tanδ-T of polymer matrix, and the inflexion point in thermal expansion curve of composite corresponded to the apex in tanδ-T curve of F-23 copolymer.