Two alfalfa varieties,Zhaodong and WL440,were taken as cold-tolerant and non-cold-tolerant varieties respectively.The germination status of the two alfalfa varieties was recorded through the chilling stress treatment of low temperature at 10℃ and 25℃ as the control,and the physiological and biochemical indexes of 7-day-old seedlings were measured.Results showed that the germination rate of alfalfa decreased significantly,the germination time was prolonged,and seedlings grew slowly under chilling stress.Chilling stress can also damage cells and cause membrane peroxidation and accumulation of reactive oxygen species.The protective enzyme system with the function of removing reactive oxygen species was also inhibited by low temperature,leading to the imbalance between the generation and clearance of reactive oxygen species,and also the oxidative damage.The cells were damaged or even dead.