Transcranial direct current stimulation (tDCS) is one of the brain stimulation techniques, which considered as an alternative treatment for Alzheimer's disease (AD). In AD, cognitive, behavior, and functional deteriorations are the result of synaptic dysfunction, neural circuit destabilization, and disrupted network activity, which are mainly caused by amyloid and tau deposition. tDCS modified neuronal resting membrane potential, synaptic plasticity, cortical neurotransmitters, astrocytes, cerebral blood flow, and functional connectivity, which could restore cognitive impairment. However, several small clinical studies that have been conducted so far have produced inconsistent results in patients with AD. Therefore, more systematic clinical studies are needed in the future.