【Background】Nowadays, chemical control plays an important role in the agroforestry production. The effects of insecticide on insects have been heavily studied, but their effects on plants have often been ignored. 【Method】Deltamethrin, an insecticide often used in agriculture, was diluted with acetone to 500 times, 1000 times and 1500 times. When the tobacco seedlings at nine-leave stage which were raised under greenhouse condition, the contents of MDA and activities of antioxidant enzymes ［superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), glutathione peroxidase (GPX)］ were tested after treated with 100 μL deltamethrin. 【Result】The results showed that deltamethrin led to lower MDA content, and the activities of SOD, CAT, APX, and GPX in tobacco leaves decreased. And it was obvious that the higher the concentration, the greater the decline. 【Conclusion and significance】The deltamethrin did not cause the oxidative stress response of tobacco seedlings. So it was ecological safety within the concentration range of 500~1500 times.