With global aging population, age-related cognitive decline becomes epidemic. Lifestyle-related factor is one of the key preventative measures. Dietary pattern analysis which considers dietary complexity has recently used to examine the linkage between nutrition and cognitive function. A priori approach defines dietary pattern based on existing knowledge. Results of several dietary pattern scores were summarized. The heterogeneity of assessment methods and outcome measurements lead to inconsistent results. Posteriori approach derives a dietary pattern independently of the existing nutrition-disease knowledge. It showed a dietary pattern abundant with plant-based food, oily fish, lower consumption of processed food, saturated fat, and simple sugar which appears to be beneficial to cognitive health. Despite inconclusive evidence from both approaches, diet and exercise, beneficial for other diseases, remains to be the two key modifiable factors for cognitive function. Large-scale prospective studies in multiethics population are required to provide stronger evidence in the future.