Simulating the salinealkali soil environment of Daqing in northeast of China which include low,middle and high concentration,we studied the effects of different concentrations and processing time(0~25 d) on each physiological index of Miscanthus sacchariflorus seedlings which basically defined the complex saltalkali tolerance range of M.sacchariflorus seedings and provided a theoretical basis for the screen of salinealkali tolerant plants and applications in landscape of energy plants like M.sacchariflorus in the future.The results showed that:(1)with the increase of mixed salinealkali stress intensity over time,the chlorophyll content of M.sacchariflorus seedlings was constantly drop.The root activity was rising with the treatments of low concentration and middle concentration over time.While it showed decreased first and then increased and decreased in the end with the treatments of high concentration.At the same time,the relative electrical conductivity and MDA content of M.sacchariflorus seedlings were also rising over time; (2)the SOD,POD,CAT,APX,GR activities,ASA and GSH contents were rising slowly in low concentration,but in the treatment of high concentration these indexes increased at first and then decreased with time passing by.The study found that M.sacchariflorus seedlings could remove excess reactive oxygen and free radicals and protect the cell structure by regulating the activities of the protective enzymes and the accumulation of antioxidants.M.sacchariflorus seedlings could effectively resist salinealkali stress of middle and low concentrations,while they have no resistance to high concentration.