The mechanical properties of hydroxyl terminated polyisobutylene(HTPB)-based polyurethane cured by a new mixed curing agent composed of isophorone diisocyanate (IPDI) and dimeryl diisocyanate (DDI) and its application in PBX were studied. Results show that when the molar ratio of isocyanate group (NCO) in the mixture of DDI/IPDI is 1/3,the tensile strength and elongation of HTPB-based polyurethane reach the maximum value of 0.427 MPa and 579.9%. When the molar ratio of NCO in DDI and IPDI is 1/1,the compressive failure load of polyurethane reaches the maximum. The elongation of HTPB-based polyurethane cured by DDI/IPDI is 2.51 times greater than that of HTPB-based polyurethane cured by toluene diisocyanate (TDI). In comparison with the compression ratio of HTPB-based polyurethane cured by TDI,the compression ratio of HTPB-based polyurethane cured by DDI/IPDI increases by 57.3%. The critical response threshold of impact sensitivity test and shear test for PBX tablets cured by DDI/IPDI increases more than 0.25 m,indicating that the impact safety of PBX is improved.