Alzheimer’s disease (AD) is one of the most common and severe dementias, severely affecting the physical and mental health and quality of life of patients and imposing a heavy burden on society. Recently, transcranial electrical stimulation (tES) has shown great potential for improving cognitive function in AD. Transcranial direct current stimulation (tDCS) and transcranial alternating current stimulation (tACS) are the two main forms of tES. The present review mainly summarizes the neuromolecular mechanisms of tDCS and tACS for the improvement of AD. Both techniques show similarities in exerting neuroprotective effects, improving cerebral blood flow to alleviate cerebrovascular dysfunction, affecting the state and function of astrocytes, affecting the levels of amyloid β protein (Aβ) and phosphorylated tau (p-tau) proteins, and affecting neuroplasticity. Specifically, tDCS improves neuronal status, inhibits neuronal apoptosis, improves cholinergic neurons and reduces oxidative stress, etc., and further exerts neuroprotective effects, but tACS mainly maintains the normal function of cholinergic neurons to exert the effects. For the alleviation of cerebrovascular dysfunction, tDCS has particular advantages in optimizing the neural vascular unit and improving the blood-brain barrier. For astrocytes, tDCS attenuates inflammatory responses by inhibiting their activation. In contrast, the effect of tACS on the activation state of microglial cells is still controversial for enhancement in AD mice and inhibition in patients. For Aβ levels, the effects of tDCS in AD patients are also inconclusive, but in AD rodents, tDCS may regulate molecular pathways related to Aβ production and degradation, thereby removing Aβ. In addition, tACS reduces p-tau levels in AD patients, but tDCS shows a trend toward reduction. In short, the effect of tES on Aβ and p-tau needs further investigation. Regarding neuroplasticity, tDCS improves cortical and synaptic plasticity, but tACS improves only synaptic plasticity. However, both techniques do not affect the molecular level associated with plasticity. On the other hand, this review has summarized some interesting findings of tES in non-AD rodents that may be relevant to the pathological mechanisms of AD. For neuroprotection, tDCS can promote neurogenesis, GABAergic and glutamatergic neurotransmission, modulate neuroprotection-related signaling pathways, reduce oxidative stress, and protect hippocampal neurons. In addition, tDCS inhibits conversion of microglia to the M1 phenotype and promotes conversion to the M2 phenotype, thereby reducing neuroinflammation. Importantly, tDCS induces changes in molecular indices associated with synaptic plasticity. These findings in non-AD rodents provide a reference for understanding the potential effect and possible mechanism of tES in AD and for exploring new approaches to treat other diseases with similar pathological features. In addition, tES has shown some effects in AD rodents, such as tACS improving plasticity, that have not been studied in non-AD rodents. These effects suggest the particular complexity of the pathological mechanisms of AD, which should be considered when applying the results of tES studies in non-AD rodents to AD rodents. In conclusion, this review provides a comprehensive overview of the neuromolecular mechanisms of tES in AD research and highlights its promise as a non-invasive brain stimulation technique in the treatment of AD. Furthermore, tES will play an indispensable role in the treatment of neuropsychiatric disorders and in the study of brain function.