Abstract: The antibacterial activity and mechanism of limonene against Pseudomonas fluorescens were studied. The minimal inhibition concentration(MIC)and growth curve were determined to characterize the effects of growth. The scanning electron microscopy,intracellular protein content and fluorescein diacetate(FDA)staining experiment were studied to characterize the morphological structure and cell membrane permeability. The effects of membrane potential,intracellular ATP content and SDH enzyme activity on the energy metabolism and tricarboxylic acid cycle of Pseudomonas fluorescens were determined. The results showed that the antibacterial effect of limonene against Pseudomonas fluorescens was good and the MIC value was 20 mL/L. After added 1×MIC and 2×MIC limonene for 3 h,the membrane potential decreased to 34.41 and 7.33 AU;after 12 h,the SDH enzyme activity decreased to 11.12 and 22.69 U/mg,respectively. The antibacterial effect was exerted by destroyed cell morphology and structure,caused severe rupture,collapse and pores in the cells,leading to the decrease of intracellular protein content,membrane potential,intracellular ATP content and SDH enzyme activity.