Abstract: The seeds of Cucumis sativus,Raphanus sativus and Brassica pekinensis were treated with water extract of Panax quinquefolium.The effects of different concentrations of water extract of healthy and root rot Panax quinquefolium on seed germination rate,seedling hypocotyl length,root length and fresh weight of 3 kinds of plants were studied,in order to analyze the differential allelopathy of Panax quinquefolium in health and root rot disease,so as to provide a basis for further screening and identification of differential susceptible substances.The results showed that the water extract of Panax quinquefolium with root rot disease significantly inhibited the seeds germination of Cucumis sativus and Brassica pekinensis at 25 000 mg ·L^-1 and 2 500 mg ·L^-1,respectively.And the highest inhibition rate was 37.25% and 24.00%,respectively,while that of healthy American ginseng had no significant inhibitory effect.In addition,the water extract of Panax quinquefolium with root rot disease significantly reduced the root length and hypocotyl length of Cucumis sativus,Brassica pekinensis and Raphanus sativus seedlings,and the growth of Cucumis sativus,Brassica pekinensis and Raphanus sativus was inhibited.But there was no obvious phenomenon in the water extract of healthy Panax quinquefolium.In conclusion,there were significant differences in allelopathic effects of water extract of healthy and root rot Panax quinquefolium on Cucumis sativus, Raphanus sativus and Brassica pekinensis seeds.