Abstract: The changes of POD’s, SOD’s activity and MDA’s content in the different geographic population of Leymus chinensis were measured after treated by polyoxyethylene glycols (PEG) of different concentrations for twenty hours and forty hours. The results showed that the responses of POD’s, SOD’s activity and MDA’s content in L. chinensis from different geographic populations were different. Using UPGMA, we found that those four geographic populations could be classified into three groups according to the changes of POD’s, SOD’s activity and MDA’s content.