Abstract: In order to improve the enzyme activity of produced amylase Bacillus subtilis N21, this strain was mutated with UV. And some characteristics of amylase were studied. The results showed that the amylase activity of mutant increased from 32.96 U/ mL to 86.24 U/mL, which increased by 161.65% than that of the original strain. The optimal reaction temperature was 35 ℃, the optimal pH value was 7.0. And The amylase activity was stable under the conditions of 30-40℃, pH of 5.0-8.0. Ca2＋and Mn2＋ could activate amylase, and Cu2＋ and Zn2＋ could inhibit amylase activity. And Mg2＋ and Fe2＋ had smaller effects on amylase activity. It was indicated that a mutant strain with higher activity of high-produced amylase was screened out.