Abstract: 【Objective】 To explore the effects of low temperature stress on physiological and biochemical characteristics of quinoa seedlings, and to provide theoretical basis for exploring the cold tolerance mechanism and breeding of quinoa varieties. 【Methods】 The top 4 varieties YN₁, YN₂, YN₃ and YN₄ with strong cold resistance were selected as experimental materials through low temperature germination test of quinoa seeds selected in Yili Valley in recent years, and the seedlings were raised in nutrient soil and treated at low temperature under artificial simulated low temperature stress environment (-4℃). Normal natural temperature treatment was set as control. 【Results】 (1) Quinoa had strong tolerance to continuous low temperature treatment of -4℃. When treated with low temperature it showed significant differences in cold resistance, among which variety YN₄ had the strongest low temperature resistance, variety YN₁ had the stronger low temperature resistance, and variety YN₃ and variety YN₂ had the weaker low temperature resistance. (2) Low temperature stress could significantly reduce the net photosynthetic rate and stomatal conductance of leaves, and the photosynthetic rate decreased the growth rate due to stomatal closure. Low temperature stress had no negative effect on photosynthetic metabolism of quinoa. (3) The active substances of antioxidant enzymes were important substances to regulate the cold tolerance of quinoa, and there were significant differences in activity among varieties. The activities of SOD, POD and MDA were significantly increased by low temperature treatment, while the activities of CAT were decreased. Strains with strong cold tolerance would have low resistance to low temperature stress by increasing the activity of key antioxidant enzymes. (4) Stable isotope and stem nitrogen concentration were important criteria for measuring the low temperature tolerance of quinoa. Low temperature treatment significantly reduced water and nitrogen metabolism of quinoa. 【Conclusion】 Low temperature resistant varieties could alleviate the damage caused by low temperature by accelerating water absorption and nitrogen metabolism. The results showed that quinoa was more tolerant to low temperature stress, but the tolerance degree of different varieties was different.