The invention relates to an application of a compound 3,4,8,9,10-pentahydroxyl dibenzotriazole[b,d]pyran-6-actone in preparing an antibacterial drug. The compound is firstly separated from mature fruits of Burma terminalia citrina (Gaertin) Roxb. According to the experiment, the compound has relatively good inhibition effect on secretion of toxic proteins SipA, B, C and D of salmonella T3SS, doesnot have inhibition effect on growth of salmonella, and inhibits invasion, on HeLa cells, of salmonella by inhibiting transfer of toxic proteins. Therefore, the compound 3,4,8,9,10-pentahydroxyl dibenzotriazole[b,d]pyran-6-actone can be used for preparing the antibacterial drug, especially can be used for preparing a gram-negative pathogenic drug.