In this paper,first,the chemical components of the tea tree oil extracted from Melaleuca alternifolia introduced from Australia and planted in Yulin,Guangxi,China,were analyzed by means of GC/MS.Next,the physical and chemical parameters of the tea tree oil were measured and were compared with the data set by ISO international standard.Then,by using Escherichia coli and Staphylococcus aureus as the indicator bacteria,the antimicrobial activity of the tea tree oil was investigated,and the corresponding minimum inhibitory concentrations（MIC） were investigated by means of mixed medicament method.Finally,the effects of pH value,salt dosage and sucrose dosage on the antimicrobial activity were analyzed.The results show that（1） in the tea tree oil,the dosage of non-characteristic composition,namely 1,8-cineole,is up to 72.49%,while that of the characteristic composition,namely terpinen-4-ol,is only 0.78%;（2） most physical and chemical parameters of the tea tree oil are not within the region set by ISO standards;（3） the MICs of the oil for Escherichia coli and Staphylococcus aureus are both 4.00 mL/L,which means that the oil is of strong antimicrobial activity;（4） the antimicrobial activity of the tea tree oil keeps strong when the pH value varies from 5 to 10;and（5） there exists obvious synergism between salt or sucrose with certain mass fraction and the tea tree oil for bacterium inhibition.Thus,it is concluded that the introduced Melaleuca alternifolia is possibly a variety,but the variety does not result in the degradation of antimicrobial activity of the tea tree oil.