Tetraacetyldibenzylhexaazaisowurtzitane (TADBIW) is the cheapest nitrolysis substrate for synthesizing hexanitrohexaazaisowurtzitane (HNIW). The process of crystal transformation of HNIW during nitrolysis is studied. Results show that α-HNIW is obtained from nitrolysis at high temperature, and it can be transformed into γ-HNIW gradually，the crystal transformation can be completed within 3 h at 70-７５ ℃ and speeded up by the additon of γ-HNIW crystal seeds in the nitrolysis system.