Abstract: The experiments were conducted to study the influence of storage temperature on superoxide anion radical, antioxidant enzyme activities and lipid peroxidation in Elymus sibiricus seeds with different moisture content (4%, 10%, 16%, 22%, 28%, 34%, 40%), and try to explore the mechanism of seed deterioration with different moisture content. The results showed that seed germination rate decreased gradually after low and room temperature storage and germination capability of seeds with higher moisture content (16%~40%) lost significantly. The percent of dead seeds increased, SOD and MDA content generally decreased with the moisture content improved. APX (ascorbate peroxidase) and superoxide anion production rate decreased with the moisture content increasing under the low temperature. In 28% moisture content, APX and superoxide anion production rate began to rise. After stored under room temperature, APX increased in 22% moisture content, superoxide anion production rate generally declined. But in 16% moisture content, superoxide anion production rate rose dramatically and seed germination rate suddenly decreased to zero, abnormal seeds and dead seeds obviously increased. In low moisture content(4%～16%), superoxide anion radical accumulation could be the key to cause seed deterioration. But the vigor reduction of seeds with high moisture content was not related to free radical accumulation and lipid peroxidation.