Exploring novel dielectric polymer materials with high dielectric performance would play a crucial role in the high energy density capacitor applications. In this work, novel polyurethanes (PUs) for high dielectric performance were fabricated using containing polar nitrile group (-C ae N) of hydroxyl-terminated polybutadiene-acrylonitrile copolymer (HTBN) as soft segment and the hexamethylene diisocyanate (HDI), toluene diisocyanate (TDI) and methylene diphenyl diisocyanate (MDI) as hard segment component. Effect of diisocyanate chemical structure on microphase separation, crystallization, dielectric property and mechanical properties of HTBN-based PUs, and the relationship between structure and dielectric property of HTBN-based PUs were investigated. The HTBN-based PUs showed high dielectric constant (> 6.4) and low dissipation factor (< 0.077) at the frequency range from 1 to 10(6) Hz. The crystallinity, degree of microphase separation and dielectric constant of HDI-/HTBN-based PU showed higher than that of MDI/HTBN and TDI-/HTBN-based PUs. Our results indicated that the dielectric constant and dissipation factor of PUs are not only dependent on the dipole orientation of hard and soft segments, but also strongly dependent on their microstructure including degree of microphase separation and crystallinity.