To address the issue of the strong hygroscopicity of green high-energy oxidant ammonium dinitramide （ADN） limiting its engineering application， an ADN/hexamethylenetetramine （HMTA） cocrystal was prepared and its properties were studied. The cocrystal was synthesized using the solvent evaporation method. Its crystal structure， purity， thermal properties， energetic performance， mechanical sensitivity， and hygroscopicity were systematically characterized by single crystal X-ray diffraction （SC-XRD）， powder X-ray diffraction （PXRD）， Fourier transform infrared spectroscopy （FT-IR）， elemental analysis （EA）， simultaneous thermal analysis （TG-DSC）， oxygen bomb calorimetry， BAM impact/friction sensitivity tests and hygroscopicity tests. The 2D fingerprint was constructed with Crystalexplorer to study its intermolecular interactions. Results show that the asymmetric unit of the cocrystal contains two ADN molecules and one HMTA molecule， belonging to monoclinic crystal system with C2/c space group， and has a density of 1.564 g·cm^-3. The analysis of intermolecular interactions confirms the formation of N─H…N hydrogen bonds with shorter bond length and greater strength in the cocrystal. The cocrystal is a pure phase with a molar ratio of ADN and HMTA of 2∶1 from XRD and EA analysis. The melting point and initial decomposition temperature of the cocrystal are 130.2 ℃ and 168.5 ℃， which are 38.8 ℃ and 14.3 ℃ higher than that of ADN. The formation enthalpy of the cocrystal is -492.55 kJ·mol^-1， the theoretical specific impulse value is 201.07 s， the detonation velocity and pressure are 7854 m·s^-1 and 20.72 GPa， respectively. The friction and impact sensitivity of the cocrystal are 288 N and above 50 J， both higher than those of ADN. The hygroscopicity rate of the cocrystal is 0 after 153 h at 25 ℃ and 70% relative humidity， for ADN the hygroscopicity rate reaches to 20.95% after 48 h. The preparation of ADN/HMTA cocrystal effectively solves the problem of strong hygroscopicity of ADN.