In order to further develop the commercial use of Melaleuca bracteata (F. Muell), this report studied the extraction of essential oil from Melaleuca bracteata (F. Muell) leaves using ultrasonic pretreatment, cellulase-inorganic salt soaked and combined with microwave-assisted hydrodistillation. To optimize the primary contributing parameters, the Box–Behnken design (BBD) was applied. The optimum yield of essential oil was 9.61 mL/kg DW at a microwave power of 510.77 W, lithium chloride dose of 63.56 μmol, and microwave irradiation period of 46.97 min. The essential oil included a total of 41 compounds, and methyl eugenol (76.53%) and methyl cinnamate (12.62%) were the main compounds. The inhibitory impact was notable when the essential oil concentration was 1.6 mg/mL. Therefore, it has the potential to replace chemical pesticides. When the concentration of the essential oil solution was 1.6 mg/mL, the three pathogenic species of fungus (Pseudocercospora psidii, Colletotrichum eriobotryae, and Colletotrichum siamense) were greatly affected; at this dose, the fungus was unable to develop and its growth diameter was 0 mm. Additionally, the fungus's inhibition rate reached 100%. [ABSTRACT FROM AUTHOR]