Executive functions are of vital importance in the process of active cognition, which is thought to be associated with the dorsolateral prefrontal cortex. As a valid brain stimulation technology, high-definition transcranial direct current stimulation has been used to optimize cognitive function in healthy adults. Substantial evidence indicates that short-term or single anodal tDCS sessions over the left DLPFC will enhance the performance of executive functions. However, the changes in performance and cortical activation of executive functions after modulation by repeated anodal (...) HD-tDCS is as yet unexplored. This study aims to examine changes in three core components of executive functions produced by nine HD-tDCS sessions, and to use functional near-infrared spectroscopy to bilaterally record DLPFC neural activity. A total of 43 participants were divided randomly into two study groups to complete nine interventions. Our results demonstrate that the enhancement of cognitive flexibility in the anodal group was significantly better than that in the sham group. Additionally, a Stroop effect-related decrease in oxygenated hemoglobin concentration in the DLPFC was observed in the anodal group but not the sham group. In conclusion, our study found that repeated anodal HD-tDCS sessions can significantly promote cognitive flexibility, one of the core components of executive function, and that alterations in DLPFC activation can enhance our understanding of the neuroplastic modifications modulated by HD-tDCS. (shrink)