OBJECTIVE: To systematically assess the effectiveness of transcranial direct current stimulation (tDCS) on global cognition in patients with mild cognitive impairment (MCI) and Alzheimer's disease (AD). DATA SOURCES: Ten databases were retrieved for pertinent Chinese and English studies published up until February 2023. DATA EXTRACTION: Two researchers independently selected the literature, extracted the data, evaluated using the Cochrane Collaboration's quality criteria, and then cross-checked. Meta-analysis was performed using RevMan 5.4. RESULTS: 22 studies involving 1074 patients were included. Compared with the control group received the interventions such as pharmacotherapy, cognitive stimulation, et al., with/without sham-tDCS, while the experiment group received tDCS added to the interventions of the control group. The meta-analysis found that tDCS increased MMSE, MoCA, MODA scores and reduced the P300 latency scores (all P < 0.05). CONCLUSION: The tDCS can ameliorate the global cognition of patients with MCI and AD, and it has a better rehabilitation effect than non-tDCS or sham-tDCS.