In clinical practice， bipolar depression is often misdiagnosed as unipolar depression， and the misdiagnosis rate is high. Only about 20% of bipolar depression patients can be definitive diagnosed in the first year， and most patients need 7 to 10 years to be diagnosed after the first episode. Now the differentiation between two affective disorders is still mainly based on clinical symptoms and characteristics. This paper reviews the difference between unipolar and bipolar depression and the prediction of its curative effect through eventrelated potential， hoping to find an objective index that can guide the clinical differentiation and prediction of the two diseases.