Anti-N-methyl-D-aspartate receptor encephalitis is a kind of autoimmune encephalitis of central nervous system. The clinical symptoms are complex. The clinical manifestations are characterized by mental and behavioral abnormalities， involuntary movements， seizures and disturbance of consciousness. The difference of mental disorder caused by anti N-methyl-D-aspartate receptor encephalitis and functional disease and the role and significance of electroencephalogram in its diagnosis are discussed in combination with two cases.