The invention discloses a vitamin composition for improving a cognitive function of the Alzheimer's disease and purpose. The composition provided by the invention is prepared from the following components by weight: 375 to 1,500 parts of choline, 0.75 to 3 parts of folic acid, 2.25 to 9 parts of vitamin B6 and 0.009 to 0.036 part of vitamin B12. Shown by an animal efficacy assessment result of thecomposition provided by the invention, the composition can be used for obviously prolonging the step-down and step-through latent periods of a P301L mouse, that is, the passive learning and memory ability is obviously improved; after the intervention of the composition, the total inquiry time, in an eight-arm radial maze, of the P301L mouse is obviously shortened; working memory and reference memory error times are reduced, that is, the spatial learning and memory ability is obviously improved; the content of homocysteine in the serum of the P301L mouse is decreased. It is shown by an animalexperimental result that the decrudescence of the cognitive function related to the pathological change of a tau sample of the Alzheimer's disease can be obviously ameliorated when a proper amount ofthe vitamin composition provided by the invention is supplemented to the animal model P301L mouse suffered from the Alzheimer's disease.