Abstract: Alzheimer's disease (AD) is the most common neurodegenerative disease, which is mostly occurred in elderly. The clinical behavior shows cognitive and memory decline, finally to the death. It still had no fundamental treatment, so had been a major socio-economic and healthcare concern. Lower consumption of docosahexaenoic acid ( DHA) is commonly associated with higher risk of cognitive decline of Alzheimer ' s disease. People who suffer Alzheimer's disease, will get significant benefits from intake plenty of ω-3polyunsaturated fatty acids, especially DHA. The available was studied that related to this result from several aspects, and had a brief discussion about the mechanisms, which were not so clear currently. Though some studies indicated there's no relation between Alzheimer's disease and DHA consumption, we considered that most of them had experimental design insufficiency.