Objective: The Coronavirus disease 2019 (COVID-19) pandemic caused a range of mental health problems, particularly self-harm. Lockdowns are the usual methods of responding to these public health emergencies. However, the effect of the COVID-19 lockdown on self-harm remains poorly characterized. This study aimed to investigate the influence of the COVID-19 pandemic on the incidence of self-harm. The findings may inform future policy development and strategies for managing pandemic-related mental health challenges. Methods: A meta-analysis was conducted using several database searches: APA PsycINFO, Embase, PubMed, Web of Science, CNKI, and Wan Fang. Published studies with data on the incidence of self-harm during visits to medical institutions, before and during the COVID-19 pandemic, were included. The pooled risk ratio (RR) value of self-harm incidence variation before and during the COVID-19 lockdown period, expressed as the comparison of clinical institution visits before and during the pandemic, was calculated. Results: Fifteen retrospective cohort studies with observational designs involving 253,600 participants were included. The pooled RR value of self-harm incidence variation was 1.386 (95% confidence interval (CI), 1.205-1.595, I2 = 58.9%, p = 0.002). The subgroup analysis showed that "emergency department type" (p = 0.004) and "mean age of the sample" were the sources of the RR values' heterogeneity (p = 0.026). Conclusions: Our findings suggest that the lockdown during the COVID-19 pandemic was a risk factor for self-harm. Therefore, special attention should be paid to individuals visiting the emergency department and the middle-aged and elderly populations. The prospero registration: This study was registered in PROSPERO (CRD42023373026), https://www.crd.york.ac.uk/PROSPERO/view/CRD42023373026.