The rubber elasticity characteristics of polyurethane network based on HTPB-IPDI were investigated through swollen compression modulus, tensile modulus and shear modulus. Both sol-gel analyses coupled with compression test, tensile modulus and shear modulus data were used to evaluate the crosslink density and corresponding physical property of each specimen obtained via variation of NCO/OH equivalent ratio and diluent effect on rubber elasticity. The experimental results indicated that the crosslink density has an effect on the mechanical property of these elastomers and effective chain length, Mc, is closely related to tole tensile strength, modulus and elongation. The deviations from the density of elastically effective network chains between swollen compression and bulk elastomer data are due to physical constraints on the junction position imposed by surrounding chains . Diluent plasticizer (DOS) extended the rubber plateau region and lowered the value of its modulus and ifs glass transition temperature The glass transition behavior also was analyzed using thermal differential scanning calorimetry method.