Against the backdrop of rising multidrug-resistant Acinetobacter baumannii (MDR AB) threats, this study explores the in vitro antibacterial activity and mechanism of Senecio scandens (a Miao ethnic medicinal herb) crude extract. Using 10 clinical MDR AB strains, we reassessed antibiotic sensitivity and then applied microbroth dilution to determine MIC/MBC, time-kill curves for bactericidal kinetics, and SEM/TEM for structural changes. Proteomics identified downregulated proteins, cross-referenced with VFDB/CARD to target membrane-related proteins (msbA, lptD), while molecular docking validated the strong binding of linarin/hyperoside to these targets. qPCR confirmed lptD/msbA mRNA downregulation (p < 0.05) by linarin/hyperoside (MIC = 312.5 μmol/L). The extract showed concentration-dependent bactericidal effects (MIC = 640 μg/mL), disrupting cell wall/membrane integrity. This study first reveals that linarin and hyperoside inhibit MDR AB by downregulating lptD/msbA, compromising outer membrane integrity, offering novel therapeutic candidates.