The purpose of this study is to look into the antibacterial activity of Tibetan propolis and the inhibitory mechanism in Haematonectria haematococca of Dendrobium nobile. To evaluate the antibacterial activity of Tibetan propolis, two types of bacteria and three types of fungi were studied with the Oxford cup method, the fungus cake method, the minimum inhibitory concentration (MIC) and the minimum bactericidal/fungicidal concentration (MBC), respectively. The hyphal morphology, growth rate, cell membrane permeability, and respiration intensity of H. haematococca after treatment with Tibetan propolis were used to investigate the antifungal mechanism. The results showed that: (1) Tibetan propolis that had broad-spectrum antibacterial activity was significantly stronger than that of commercially available propolis. (2) On the five tested strains, Tibetan propolis extracted with 80% ethanol at pH 6 had the best antibacterial activity. (3) At a concentration of 10 mg·mL^-1 of Tibetan propolis, the mycelial growth inhibition rate was 89%, and the EC₅₀ was 2.552 mg·mL^-1; under these conditions, the morphology of the mycelium cells changed from full rupture to shriveling, which increased the cell membrane permeability and content leakage. Furthermore, the respiration intensity increased, which blocked the energy metabolism and inhibited the mycelium growth. In summary, Tibetan propolis is a natural broad-spectrum antibacterial agent with promising the development and research potential for controlling plant diseases caused by H. haematococca.