The diagnosis of autoimmune encephalitis depends on symptoms, imaging, and autoantibodies. However, the detection of autoantibodies has poor popularity, and the negative result of autoantibodies or no significant immunotherapy response in the early stage cannot rule out the disease. Cerebral MRI of intracellular antigen-related limbic encephalitis often shows abnormalities in the medial temporal lobe, while cell-surface antigen-associated encephalitis is usually normal or abnormal in areas other than the medial temporal lobe. Different autoantibody-associated encephalitis has different FDG-PET manifestations in the acute phase, but all patients with encephalitis in the later stage can have different degrees of brain atrophy, with hippocampal atrophy being more common. Therefore, imaging modalities such as head MRI play a very important role in early diagnosis. And because of it high sensitivity, FDG-PET has attracted wide attention in detecting autoimmune encephalitis. Here we review the MRI and FDG-PET findings in different types of AE, with an aim to improve its application in early screening and diagnosis of AE.