“Number four jinyan” seeds were chosen to study the poison effect of 0.5, 1.5, 2.5, 4.0 mmol/L Pb(NO3)2 and 0.5, 1.0, 1.5, 2.0 mmol/L CdCl2 on cucumber seeds during the course of germination. The results showed compared to the CK, the inhibition on growth of radicle and germ significantly increased with increasing concentration of Pb and Cd. The growth of the radicle was more significantly inhibited by Pb and Cd stress. After seven days of stress, the average length, fresh weight of seedling and the chlorophyll content of cotyledons obviously decreased with the increase of the concentration of Pb and Cd. The result observed through transmission electron microscope showed ultrastructural changes of root tip cells of seedling were unusually apparent after four days of stress, which were characterized by cell gap increasing, chromatin spilling, reducing and eventually disappearing of the mitochondria and crest. Inside the cells, the membrane structure of each organelle was severely damaged until disintegrated and disappeared. The cell wall was partly fractured and the cell structure was collapsed. The poisoning effect caused by Cd was more serious than that caused by Pb under the same experimental conditions.