Bipolar disorder (BD) is characterized by periodic alternations between depressive and manic episodes. It belongs to a complex group of severe and persistent conditions. This category includes bipolar I disorder (BDI) and bipolar II disorder (BDII). The definition of BDI hinges primarily on the manifestation of a syndromal manic episode. Conversely, BDII is characterized by the occurrence of both a syndromal hypomanic episode and a major depressive episode, which jointly constitute its defining features. BDI is the most common type in clinics. The duration of episodes and the time spent in the manic phases and depressive periods of bipolar disorder are not clearly defined for subtypes of the disorder. This paper analyzes the duration of manic episodes and depressive episodes in bipolar disorder, and explores the switch from major depression to bipolar depression. By analyzing and comparing the data and results in essays, it is still hard to tell the exact duration and the occurrence of the episodes. But the effects of drugs can be summarized during the treatment of bipolar disorders. At the same time, it discovers that during treatment of major depression, bipolar disorder occurs. In conclusion, the duration is different for different people, and it depends on many subjective influences. During treatment of major depression, the transition from major depression to bipolar depression will happen indeed, but the probability is very small. This research may provide a new concern that doctors and scientists should pay more attention to the treatment of such mental diseases and keep an eye on the switch.