Abstract: DHA is very long chain polyunsaturated fatty acids that provide important human health benefits.Thraustochytriales have become the current research hot spot because of its high level of DHA. In this article the sources of DHA and microbial metabolic pathways were introduced, and the international research progress on DHA were summarized.The various factors that affect DHA fermentation were also studied and it was pointed out that the future work should emphasis on screening high- yielding strains and studying the metabolic pathways, the scale- up cultures, and the transgenic production DHA.