The waterborne polyurethane (WPU) was synthesized from isophorone diisocyanate (IPDI), polypropylene glycol (PPG), dimethylolpropionic acid (DMPA) and 1,4-butanediol (BDO) under acetone reflux. The cast films obtained from it were characterized by Fourier transform infrared (FTIR), nuclear magnetic resonance (1H NMR) and differential scanning calorimetry (DSC). The curve of DSC presented a bimodal profile. It showed that the waterborne polyurethane resin degraded obviously at about 305°C and 381°C, which was an endothermic course. The scanning electron microscopy (SEM) micrographs revealed that hexanitrohexaazaisowurtzitane (HNIW) was coated with waterborne polyurethane by means of water volatilization. The impact sensitivity experimental results indicated that the characteristic height H50 of HNIW coated with waterborne polyurethane increased from 25.1cm to 34.2cm. That is, the waterborne polyurethane can decrease the impact sensitivity of HNIW.