Bacillus subtilis used as probiotic was widely applied to the aquiculture to purify the water with the needs of healthy breeding. In this paper twelve Bacillus subtilis strains were isolated from activate sludge of breeding shrimp pond,breeding fish pond and polluted river. H4and H5with high amylase activity were screened from the isolated strains by amylum degradation experiment and the activities of amylase were 38. 66,37. 10 U/ mL,respectively. The mean of ul2 traviolet continuous induced mutation was used on H4and H5. The results showed that the extracellular amylase activities of first mutant strains H4Ⅰ and H5Ⅰ were 41. 36 and 41. 32 U/ mL,which were 107 % and 111 %of initial strains. While the extracellular amylase activities of second mutant strains H4Ⅱ a,H5Ⅱ a and H5Ⅱ b were increased to 147 %,136 % and 135 % of initial strains,and the activities of amylase were 56. 95,50. 47 and 50. 02 U/ mL,respectively. The results indicate that ultraviolet continuous induced mutation would be in favor of the amylase producing of mutant strain.