Solubility of hexanitrohexaazaisowurzitane （HNIW） and its changes with temperature in three kinds of different concentrations of nitric acid were measured.The process of crystal transition from α, γ-HNIW to ε-HNIW in nitrate acid was studied. ε-HNIW with different crystal quality were obtained by changing concentration of HNO₃, temperature of adding crystal seeds, stirring rate. ε-HNIW is obtained in 90% nitric acid when the temperature of adding crystal seeds is in the range of 34-40 ℃ . Its yield and purity is over 98%，99% respectively, and acid number is below 2‰ (as HNO₃).