Abstract: Using water extraction method to extract the allelopathic substances of invasive plant Bidens frondosa leaf and stem, by contrast test, the effects of different concentrations of aqueous extract of stem and leaf of Bidens frondos on seed germination and seedling growth of wheat and barley were studied.The results showed that the extract of Bidens frondos plants had significant inhibition on the germination of barley seeds, but not on the germination of wheat seeds.Except for 50 g/L extract, the other treatments significantly inhibited seedling height and root length of barley and wheat.The extracts could inhibit the differentiation of the roots of 2 crops.Among them, the inhibition on wheat root differentiation is relatively large.The synthetic allelopathic effect of Bidens frondosa extract on wheat and barley is inhibitory and the inhibition to barley is greater than that of wheat.