Abstract: In order to know the nemsticifal activities substance and the mechanisms of Datura metel Linn, total alkaloids from the leaf of Datura metel Linn was extracted and identified, and studied the mechanism of it by determining the activity of Ache and the Ach content of Meloidogyne incognita. The results showed that alkaloids played a determinant role in nematocidal activity. It suppressed the activity of AchE , increased the number of Ach, could attack the nematode neural system.