Since the global COVID-19 pandemic, SARS-CoV-2 infection, which causes COVID-19, has been associated with a range of diseases whose atypical manifestations have been increasingly reported. The mild encephalitis or encephalopathy associated with reversible corpus callosum lesions or mild encephalitis/encephalopathy with reversible splenial lesion (MERS) is a rare clinical and radiographic syndrome. At present, the pathogenesis of MERS caused by COVID-19 is still unclear, and its pathogenesis may include hypoxic damage, inflammatory response, immune disorders, changes in osmotic pressure, excitatory amino acid toxicity, oxidative stress and functional abnormalities of renin-angiotensin system. This paper reports a case of severe COVID-19 complicated with MERS, and discusses the pathogenesis from a pathophysiological point of view.