Based on the field experiment,the description of the vertical distribution of immature staffs of the dia-mondback moth,Phtella xylosella within some cruficerous vegetables that are flowering Chinese cabbage,Chinese kale and broccoli was given.The results showed that the eggs were mainly laid on the 2nd leaf and the larvae concentrated in the growth point and the youngest leaves,while the pupae were all distributed within the plants.In the other hand,the movement behaviors of this pest within plants and its mechanism were disscussed in this paper.