Brevibacterium flavum 1000 was used as the original strain and site-specific mutagenesis was performed in its ilvBN gene，resulting in an anti-feedback inhibition gene ilvBN'． The gene ilvC' encoding acetohydroxyacid isomeroreductase was obtained by site-directed mutagenesis from ilvC． The gene ilvBN'C' was obtained by overlap extension PCR from ilvBN' and ilvC，and then inserted into E． coli-B． flavum shuttle expression vector pXMJ19 to construct a recombinant plasmid pXMJ19-ilvBN'C'． The recombinant plasmid was subsequently transformed into B． flavum MH-1000，resulting in the strain MH-1032． The results from fed-batch fermentation experiments in 50 L fermenter indicated that the L-valine productivity of MH-1032 ( 38． 4 g /L) was increased by 9． 1% in contrast to that of MH1000 ( 35． 2 g /L) in 72 hours，and the conversion of glucose to L-val increased from 21． 7% to 25． 8%．