Abstract: Indoor Petri dish bioassay was adopted to study allelopathy actions of Veronica didyma Tenore and the results showed that the extract solution of Veronica didyma Tenore by water remarkably inhibited the growth of wheat seedlings and this inhibit became strong as the concentration of the extract solution increased. The extract solution inhibited the growth of wheat roots more strongly than the growth of wheat leaves. Some physiological and biochemical indexes of treated wheat indicated that the extract solution of Veronica didyma Tenore by water increased the vigor of treated wheat roots, and reduced the content of soluble protein of treated wheat leaves; it also reduced the content of chlorophyll relatively. The activity of catalase(CAT) in leaves was reduced apparently, while the activity of peroxidase(POD) and (SOD) was increased.