In order to explore the Allelopathic effects of Phytolacca americana root extract on seed germination andseedling growth of different crops,taking radish,wheat and cotton as materials,the effects of different concentra-tions of Phytolacca americana root extract on seed germination,seedling growth,protective enzyme activity,osmot-ic adjustment substance and malondialdehyde content of three crops were studied by means of culture dish germina-tion test. The results showed that the extracts of Phytolacca americana root had different degrees of inhibition onseed germination rate,germination potential,germination index,seedling height,root length and fresh weight of three crops. The higher the concentration of extract,the stronger the inhibition. With the increase of extract concentration,the activities of SOD and POD in radish and wheat and SOD activity in cotton first increased and then decreased,while the activity of POD in cotton always showed aincreasing trend. The contents of soluble sugar,soluble protein,Pro and MDA in wheat and cotton increased gradually,while that radish increased first and then decreased. The results showed that the extracts had stronger inhibition on radish seed germination and seedling growth than on cotton seed.