To study the antioxidant effect of crude polysaccharides from grape seeds(GSCPs) in vitro and its in vivo antioxidant activity on Caenorhabditis elegans(C.elegans), GSCPs were extracted and isolated by water extraction and alcohol precipitation. The scavenging effect of GSCPs on 1,1-diphenyl-2-picrylhydrazyl(DPPH) free radical and hydroxyl free radical as well as their inhibitory effect on DNA oxidative damage were detected in vitro. The antioxidant capacity of GSCPs on cellular level was investigated by H₂O₂-induced oxidative damage model of RAW 264.7 macrophages. In addition, the antioxidant function in vivo of GSCPs was studied by C.elegans. The results of in vitro experiment demonstrated that GSCPs could effectively scavenge free radicals and inhibit oxidative damage to DNA. The scavenging activities of 0.4mg/mL GSCPs for DPPH and hydroxyl radical were 84% and 89%, respectively. GSCPs could attenuate H₂O₂-induced oxidative damage in RAW 264.7 macrophages by decreasing reactive oxygen species(ROS) levels and increasing the activities of superoxide dismutase(SOD) and glutathione peroxidase(GSH-Px). Compared with H₂O₂ treated group, the activity of SOD and GSH-Px increased from 81.1% to 96.3% and from 92.1% to 99.6%, respectively after treated with 0.2mg/mL GSCPs. GSCPs could prolong C.elegans lifespan, improve the ability to resist acute oxidative stress, and effectively remove ROS in C.elegans. Compared with the control group, the average lifespan of C. elegans and the average survival time under acute oxidative stress were prolonged by 27.67% and 33.58%, respectively in the 0.8mg/mL GSCPs treated group. In contrast, GSCPs could cause 56.33% reduction in ROS levels of C.elegans. Therefore, GSCPs showed good antioxidant activicy in vivo and in vitro, which could be used as potential antioxidant ingredients in functional foods.