Abstract: The present invention discloses an application of norharmane in improving activity of an antibiotic in resisting bacteria, when norharmane of the present invention is combined with polymyxin B, imipenem-cilastatin sodium or levofloxacin, it can enhance antibacterial activity of the antibiotic against drug-resistant Pseudomonas aeruginosa, produce a synergistic antibacterial effect, and significantly improves the killing ability of antibiotics against drug-resistant Pseudomonas aeruginosa to reduce the amount of antibiotics needed for achieving the same therapeutic effect, thereby providing a research direction for the development of new drugs and new use of old drugs.