Abstract: In order to explore the toxic mechanism of heavy metal pollution on plants,in this paper,the seeds of mung bean were treated with different concentrations of lead nitrate solution to simulate heavy metal stress,and the effects of salicylic acid（SA）on the germination and seedling growth of mung bean under heavy metal stress were studied.The results showed that with the increase of the concentration of lead nitrate stress,the physiological and biochemical indexes of mung bean seed,such as germination potential,germination rate and root length,decreased gradually.The abnormal phenomena such as chromosome ring,chromosome bridge and micronucleus appeared in root tip cells during mitosis.150 mg·L^-1 lead nitrate could significantly inhibit the germination and growth of mung bean seeds.However,the 50 mg·L^-1 SA could alleviate the inhibition of seed germination and growth of mung bean under the stress of lead nitrate,and the abnormal condition of root tip chromosome division was weakened.Salicylic acid could increase the stress resistance of plants to resist the persecution of environment.