A strain with highest in vitro inulinase activity was selected from 18 strains of Aspergillus niger. Tthe enzyme activity of the strain No.08013 was 3.01 U/mL. The mutant strain of Aspergillus niger was screened by low energy ion beam N~+. When the N~+ energy of 10 Kev injected into the implantation chamber of the vacuum degree is 10~(-3) Pa,the pulse dose was 10~(14) N~+/cm~2 s,N~+ injection at a dose of 60×2.6×10~(13) N~+/cm~2,screened a strain of highest activity of endo-inulinase,4.20 U/mL,numbered 08-D...