Method of acid- alkali titration is traditional analysis method. It is typical of manipulation easy, little error and excellent accuracy. In this paper, by using the method of acid-alkali titration, the acid number for ε-hexanitrohexaazaisowurtane（HNIW）obtained in two system（nitric acid and ethyl acetate and chloroform) was determination respectively. Different conditions were determined. For ε-HNIW prepared in nitric acid system, titration conditions are 5-6 g HNIW with 80 mL acetone as solvent and neutral red-methylene blue as indicator. For ε-HNIW prepared in EtOAc-CHCl3 system, conditions are 5-6 g HNIW with 50 mL acetone as solvent and resorcin blue as indicator.