Abstract: 4′-Epidaunorubicin is major precursor for the semisynthesis of epidoxorubicin，a clinically important antitumor antibiotic.By means of homologous recombination used for dnmV replacement and aveBⅣ integration into daunorubicin-producing strain，a mutant strain，named mHJ-02-30-1，was obtained that produces 4′-epidaunorubin.An in-frame knock-out plasmid was transformed into mHJ-02-30-1 to delete the dnrU gene fragment encoding 153 amino acids.The genetic engineering strain mYG1116E，a dnrU gene inactivation mutant，was constructed by homologous recombination，which increased the 4′-epidaunorubin production by 40% compared with the original strain.