Fucoidan has various physiological activities, and its structure is also different according to different brown algae. In this study SNF (Sargassum Naozhouense fucoidan) was extracted by acid extraction method, and its relative molecular weight was determined to be 631.40 kDa. The structure contains 42 % hydroxyl with sulfate group, and it is mainly composed of fucose, galactose and xylose. In the activity study, intracellular oxidative stress is closely related to angiogenesis. The results show that SNF could ameliorate cellular oxidative stress injury by inhibiting the production of intracellular reactive oxygen species (ROS), nitric oxide (NO) and DNA damage in HepG2/CYP2E1 cell. In addition, SNF can reduce the activity of Matrix Metallopeptidase (MMP-2/9), and inhibit hypoxia-inducible factor-1α (HIF-1α) expression by regulating the downstream PI3K/AKT and Ras/MAPK pathways, thereby preventing vascular endothelial growth factor (VEGF) production, and further inhibits VEGF receptor-2 activation and ultimately inhibits angiogenesis in HT1080 and HUVECs. Therefore, SNF has the potential to develop tumor prevention functional substances and can provide theoretical basis for the high-value comprehensive utilization of brown algae.