The effects of light stress with different light intensities (120~270 μmol/m2?s) and photoperiods (light/dark: 0/24-24/0 h) on the astaxanthin accumulation, superoxide dismutase (SOD) and catalase (CAT) activities, total antioxidant capacity (T-AOC), and superoxide anion free radical (O2-?) scavenging ability of Haematococcus pluvialis were examined. The results showed that at green, brown, and red cell stages, a higher light intensity led to higher astaxanthin content and greater T-AOC and O2-? scavenging ability. The activities of the antioxidant enzymes (SOD and CAT) increased at the green cell stage and decreased at the red cell stage, with increasing light intensity. The highest astaxanthin content and greatest T-AOC and O2-? scavenging ability were obtained at the red cell stage, whereas the highest antioxidant enzyme activities were obtained at the brown cell stage. when H. pluvialis grew for ten days under different photoperiods and a light intensity of 270 μmol/m2?s, the astaxanthin content and T-AOC and O2-? scavenging ability increased with the extensions of the daily illumination period, whereas the activities of the antioxidant enzymes decreased after the initial increase. In summary, H. pluvialis showed the highest astaxanthin content and antioxidant capacity after continuous illumination at a light intensity of 270 μmol/m2?s for ten days. This finding provides a new reference for the production and application of astaxanthin as a natural antioxidant food additive.