Transcranial direct current stimulation (tDCS) is a non-invasive technique that uses a weak current (1 to 2 mA) to modulate cortical neuronal activity. Two electrodes placed on the scalp act on the cerebral cortex with a weakly polarized direct current. Neurophysiological experiments have demonstrated that neuronal firing increases when the positive or anode of the electrode is close to the neuronal cell or dendrite and decreases when the opposite is true. With proper electrode placement, tDCS can alter the excitability and functional properties of visual, somatosensory, and prefrontal cortical neurons; stimulating the posterior part of the lateral perisylvian area can enhance language processing; applied to motor and visual cortices, tDCS can facilitate learning processes. Thus, tDCS is a technique capable of inducing changes in cortical functional plasticity. Clinical applications of tDCS in brain injury: 1. Motor impairment: Recent studies have shown that stimulation of the damaged hemisphere in stroke patients with anodal tDCS can promote the recovery of hand function on the affected side. Functional recovery after stroke depends on the balance of neural network activity, both in the damaged and undamaged hemispheres. Increasing the activity of the damaged hemisphere may promote functional recovery. 2.Spasticity: During stroke recovery, there is over-activation in the S1M1 area of the affected cerebral hemisphere; tDCS inhibits S1Ml and its surrounding areas in the affected upper limb, probably by suppressing the over-activation of S1Ml, thus changing the imbalance between the central inhibitory system and the easy-access system, and achieving the effect of suppressing muscle spasticity in the affected upper limb. 3. Aphasia: Neuroimaging studies have shown that the realization of speech naming function requires the mobilization of an extensive and complex system of brain neural networks to participate, including the left prefrontal and temporal lobes. Studies have shown that anodal tDCS stimulation of left-side speech-related brain regions significantly improves patients’ speech functions. In dealing with difficult, severe and rare speech dysfunction, the rational application of tDCS on cortical function regulation may achieve a greater breakthrough than traditional treatment methods. 4, cognitive impairment: Specific cognitive rehabilitation training has a significant improvement on cognitive dysfunction, and the application of tDCS can tap the potential of cognitive recovery to a greater extent. tDCS stimulates the temporoparietal area of Alzheimer’s disease (AD) patients, and increasing the excitability of the temporoparietal area can improve the recognition memory ability of AD patients. Anodal tDCS stimulation of the left dorsolateral prefrontal lobe (DLPFC) significantly improved memory for word pairs.