Using the method of small glass, bioassay was conducted to study the activity of the essential oil extracted from Artemisia scoparia at different concentration on growth inhibition of root and stem of the weed Echinochloa crusgalli. The results showed that the essential oil inhibited the growth of root and stem of the weed under light and non-light, while the activity was higher under light than that under non-light. Activity assayed of several protective enzymes indicated that except the superoxide dismutase (SOD) was inhibited, the activities of glutathione-S-transferase (GST), glutathione peroxidase (GSH-Px) and peroxidase (POD) were induced and enhanced greatly by essential oil in the callus of E. crusgalli under light.The observation under electron microscope showed that the membrane in cell of callus exposed to the essential oil was damaged under light. The cells of callus were destroyed totally because of a great stress of oxidation in the callus caused by the essential oil. It was indicated that the biological membrane was the main target for the essential oil action.