Abstract : This paper presents the first phase of development of a multiscale numerical method oper-ating at the microstructureal level for a TATB-based pressed plastic-bonded explosive. It uses a virtual model of microstructure mimicking the grain size distribution of the actual material, and a Fourier-based numerical scheme. At present, the method works with sim-plified microstructure and linear anisotropic thermoelastic behavior for the constituents. Neglecting the inter-granular binder leads to fairly overestimated values for isotropic elas-tic moduli and volumetric coefficient of thermal expansion. A first attempt to include the binder yielded much more realistic predictions for elastic moduli, but not for the volumet-ric thermal expansion coefficient. The origin of this discrepancy is thought to lie in the behavior of constituents.