The linear coefficient of thermal expansion (CTE) and the theoretical density are important for energetic materials. To obtain the CTE and theoretical density of 2,2',4,4',6,6'-hexanitrostilbene (HNS), X-ray powder diffraction (XRD) together with Rietveld refinement was employed to estimate the dimension and density change at a crystal lattice level, in the range of temperature 30-240 A degrees C. The CTE of a-, b-, c-axis and volume were obtained as 7.6719 x 10(-5)/A degrees C, 6.8044 x 10(-5)/A degrees C, 1.1192 x 10(-5)/A degrees C and 16.725 x 10(-5)/A degrees C, respectively. Also, the possible reasons for the expansion property of HNS have been discussed by comparing its structure with 1,3,5-triamino-2,4,6-trinitrobenzene (TATB). Based on the refined lattice parameters, the theoretical densities of HNS at various temperatures were obtained. By extrapolation of linear fitting the theoretical density of HNS at 20 A degrees C was gotten as 1.7453 g/cm(3). Furthermore, a good thermal resilience of HNS has also been observed when the temperature returned from 240 to 30 A degrees C.