With the increasing prominence of population aging, the cognitive decline of the elderly has gradually become a hotspot of clinical research. As a traditional rehabilitation exercise, Tai Chi has been proved to have a positive effect on improving cognitive function and delaying cognitive decline in the elderly. However, the related brain function mechanism is still unclear. In this paper, we collected studies which observed the changes of Tai Chi on brain regions related to cognitive function in the elderly using magnetic resonance imaging (MRI), electroencephalogram (EEG) and functional near-infrared spectroscopy (fNIRS). We summarized relevant studies from perspective of structural and functional changes in the brain. The results showed that Tai Chi may delay and improve cognitive decline in the elderly by reshaping the structure and function of brain regions related to cognitive function such as memory, attention and execution. The effect of Tai Chi for cognitive function may be associated with positive regulation of cardiovascular function, emotion and meditation level of the elderly. In addition, the improvement of cognitive function further enhances the balance of the elderly. We also found that practice time, frequency and intensity of Tai Chi could be factors influencing the improvement of cognitive function and brain function in the elderly.