Mixotrophic cultivation of Haematococcus is efficient to increase astaxanthin productivity. However, application of this technique in open bioreactors is restricted because of bacterial contamination. In this study, mixotrophic cultivation of Haematococcus was carried out successfully in an outdoor raceway pond. The Haematococcus cells grew on light first, and then acetate/acetic acid was supplemented when nitrate was depleted from the culture media. Under such conditions, Haematococcus cells grew on intracellular nitrogen pool, while bacterial reproduction was limited. The average astaxanthin productivity reached 140 mg m？2day？1, which is about 1.2 times that of the simple phototrophic cultivation. This study explores a potential way to enhance astaxanthin productivity, and the results are helpful to the development of the Haematococcus industries.