Analyzed the nutritional value and antioxidant capacity of Shepherd’s purse seed. There were many kinds of nutrients in the seed of Shepherd’s purse. The content of crude fat ranked the first with 37.6 g/100 g, and among the crude fat, unsaturated fatty accounted for 87.28%, α-linolenic acid and linoleic accounted for 32.80% and 20.12%, respectively. The erucic acid took the only left 0.30%. The crude protein content was 18.7 g/100 g. The first limiting amino acid of crude protein was methionine, and its amino acid score was 64. Among the group of Vitamin E, contents of E-vitamin E was the highest at 14.0 mg/100 g. The contents of K、Ca、Mg were high among the minerals. The water extracts of Shepherd’s purse seeds had the strongest ability of scavenging DPPH·, which was about 1/20 of ascorbic acid. To H₂O₂, OH· and NO ,its capacity was about 1/40 to 1/20 of ascorbic acid.