In order to reducing the acidic impurity B₂O₃ and H₃BO₃，the amorphous boron powder was neutralised respectively with ammonia in gas phase（B-1），ammonia in liquid phase（B-2）and sodium hydroxide in solution（B-3）.The rheological characteristics of B-1，B-2 and B-3 with HTPB were researched. The results indicate that the apparent viscidity and yield value of B-1/HTPB mixture increase rapidly with mixing time increasing，those of B-2/HTPB mixture increase slowly and those of B-3/HTPB mixture almost don′t increase. The mechanisms of three neutralization methods of the amorphous boron powder were discussed through acidity meter，TG，IR and XRD analysis. The results show that the improvement in rheological property of B-1/HTPB mixture is due to NH₃ absorbed to the boron surface，which maybe obstructs the reaction between H₃BO₃ and HTPB，but disabsorbs in mixing process and results in the gelatinization of B-1/HTPB mixture. Due to a soluble compound formed by the reactation between ammonia and H₃BO₃ on boron surface，the rheological property of B-2/HTPB mixture improves. The better rheological property of B-3/HTPB mixture is owing to the soluble NaBO₂ formed by the reactation between NaOH and H₃BO₃，which reduces the content of H₃BO₃ on the boron powder.