Dairy mastitis is a disease of dairy cattle caused by a variety of pathogenic microorganisms which has biought huge economic losses aused huge economic losses to the world. In this paper, Harmine derivatives and tetrahydro-β-carboline derivatives synthesized by the splice method are shown to have a good inhibitory effect on the pathogenic bacteria of dairy mastitis. The results of a bacteriostatic test on pathogenic bacteria of dairy cow mastitis (S. dysgalactiae, S. pyogenes, B. subtilis and P. vulgaris) showed that compound 7l had the best bacteriostatic effect on Streptococcus dysgalactiae, with a mic value of 43.7 μ g/mL. When the concentration of 7l was 1 × MIC and 2 × MIC, it had a significant inhibitory effect on Streptococcus dysgalactiae, and there was almost no growth of Streptococcus dysgalactiae at 4 × MIC. The binding properties of target compound 7l to amine oxidase [flavin-containing] A protein were simulated by the molecular docking technique. The ligand 7l achieved strong binding with the receptor through three hydrogen bonds. The hydrogen bonds were amino acid residues thr-52, arg-51 and ser-24, which are the main force for the compound to bind to active sites.