Anti-N-methyl-D-aspartate receptor (NMDAR) encephalitis is the most prevalent type of encephalitis. Investigating the pathogenesis of anti-NMDAR encephalitis will enhance our understanding of this disease and play a central part in providing reasonable treatment for the patients. The pathogenesis is elucidated as follows: (1) the findings of the relationship between anti-NMDAR encephalitis and tumors; (2) further research on the relationship between anti-NMDAR encephalitis and tumors; (3) NMDAR epitopes and the autoimmunity of patients; (4) the interaction between antibody and NMDAR; (5) the pathogenesis of anti-NMDAR encephalitis without tumors. This review gives a brief introduction to the methodology and way of finding out the valuable clinical problems and making a clear and explicit explanation of them by exhibiting the process of discovering the disease, disclosing its relationship with tumors, and investigating its pathological and molecular mechanism. Current studies have demonstrated that anti-NMDAR encephalitis is an autoimmune disease of the nervous system that is closely associated with tumors, particularly ovarian teratoma.