γ-Hexanitrohexaazaisowurtzitane(HNIW) with different contents of pentanitromonoacetylhexaazaisowurtzitane (PNMAIW) was prepared, and crystallized to ε-HNIW in ethyl acetate/trichloromethane system. Results show that the content of PNMAIW decreases by less than 1% through crystallization, and affects the time of crystallization.