We analyzed the characteristics of Hashimoto’s encephalopathy in child.A child was diagnosed with Hashimoto’s encephalopathy accompanied by arrhythmia starting with epilepsy and high fever. No significant abnormality was found in the cerebrospinal fluid analysis of two lumbar punctures. The antibodies against autoimmune encephalitis in the blood and cerebrospinal fluid were negative. The titers of anti-thyroglobulin antibody and thyroid peroxidase antibody were significantly higher than normal. Brain MR showed diffuse symmetrical swelling of bilateral cerebral cortex. 24h ambulatory electroencephalogram (EEG) showed that δ activity of the head was not a typical spike-slow wave discharge. 24h ambulatory electrocardiogram showed sinus arrhythmia and frequent atrial premature beats. Paroxysmal atrial tachycardia. The patient finally diagnosed as Hashimoto encephalopathy with arrhythmia.After 5 days of methylprednisolone 20 mg/ (kg.d) shock therapy, intravenous human immunoglobulin of 2g/kg, prednisone 2 mg/ (kg.d) maintenance therapy,sotalol 40 mg oral,2 times/ d,Wenxin granule 1.25g, 3 times / d, the children were discharged from hospital.Hashimoto encephalopathy accompanied by arrhythmia in child starting with epilepsy and high fever was rare. Routine screening of thyroid function and thyroid peroxidase antibody can improve prognosis by early diagnosis and treatment.