Abstract：The SCF-MO-AM1 method and MM-COMPASS force field have been applied to the calculation on TATB (1,3,5-triamino-2,4,6-trinitrobenzene) and a series of PBX (Polymer Bonded Explosive). A great deal of parameters of structures and properties including binding energies of PBX were obtained using full geometry optimization on the basis of atomic cluster matching size model. It is found that there is good linear relation between binding energies calculated by AM1 and MM methods. Atomistic molecular dynamics (MD) has been used to simulate mechanical properties of TATB and a series of PBX. Elastic coefficients and effective isotropic elastic constants, such as tensile module, bulk module, shear module, and Poisson's ratio were determined at room temperature and pressure. The results indicate that elastic properties of TATB can be greatly improved by adding a little amount of polymer.