Polymer bonded explosives are composites containing elastic energetic particles in a viscoelastic binder. The volume fraction of the elastic particles in PBX is normally greater than 80%, therefore using the classical analytical meso-mechanics model (Hashin-Shtrikman) to estimate the effective elastic modulus of TATB-based PBX is quite inaccurate. A new term named “interface bonding parameter” which contains the density of the bulk PBXs was promoted and a modified model of Hashin-Shtrikman was obtained. The samples with different densities were prepared, and their elastic modulus was measured, and the modified coefficients of the model were obtained to be 0.813（ρ/ρ₀）8.64or 0.296（ρ/ρ₀）8.68. The elastic modulus was calculated by the classical Hashin-Shtrikman model and by the modified model respectively. It shows that the modified model with “interface bonding parameter” can give more accurate results compared to that with the classical Hashin-Shtrikman model. The effective elastic modulus decays exponential with the decreasing of TATB-based PBX density, and the effective bulk modulus and the effective shear modulus are influenced by density to the same degree,and the exponents are about 8.6. The predicting and the experimental results are only 1% apart. It proves that the modified Hashin-Shtrikman can be used to predict the effective modulus of double-composition PBXs.