Abstract:The antimicrobial activities of three essential oils and their chemical constituents against five pathogenic bacteria were studied by filter paper method，broth dilution method and dot seed method in vitro.The chemical constituents were identified by gas chromatography-mass spectrometer （GC-MS）under the optimum analytical conditions，and the relative percentage of each compound in volatile oil was determined by peak area normalization method.The results showed that 9.5 % of the essential oils of oregano，citronella and clove could kill all Staphylococcus albicans and Candida albicans；4.75 % of the essential oils of oregano，citronella and clove could kill all Staphylococcus aureus；4.75%of the essential oils of oregano and clove could kill all Escherichia coli，but the killing concentration of citronell was relatively weak；the killing concentration of three essential oils to Pseudomonas aeruginosa was higher than 9.5%.The results of GC-MS showed that the main components of oregano were dipentene（33.93%），thymol（19.12%），4-terpene alcohol（14.92%）and α-pinene（10.87%）；The main components of clove were eugenol（86.54%）and 1-caryophyllene（10.41%）.Citronella mainly included citronellal（31.38%）and geraniol（18.43%）.Plant essential oil had broad-spectrum antimicrobial activity.