Objective To explore the functional connectivity differences of amygdala subregions in unipolar depressive disorder（ UDD） and bipolar depressive disorder（ BDD） patients with insomnia of varying severity. Methods This study was a cross-sectional study. A total of 147 outpatients or inpatients at Beijing Anding Hospital， Capital Medical University， between March 2021 and June 2022 were recruited， including 60 patients with BDD and 87 patients with UDD. At the same time， 53 participants for the healthy control group were recruited through public advertisements. General information， clinical data， and resting state functional magnetic resonance imaging（ fMRI） data of all subjects were collected. Based on the insomnia subscale of the 17-item Hamilton Depression Rating Scale（ HAMD-17）， the two groups of patients were divided into a low insomnia group（ LI group， HAMD-17 insomnia subscale total score ≤ 3） and a high insomnia group （HI group， HAMD-17 insomnia subscale total score ≥ 4）. Using the 8 subregions of the amygdala as seed points， functional connectivity between these seed points and all other voxels in the whole brain was calculated， and one-way analysis of covariance was used for intergroup comparisons. After identifying significant results， Spearman correlation analysis was further used to calculate the correlations between functional connectivity of amygdala subregions and patients' symptoms of depression， anxiety， and mania. After screening， 28 patients were enrolled in the BDDHI group， 28 in the BDDLI group， 38 in the UDDHI group， and 41 in the UDDLI group. Results There were statistically significant differences in the adjusted HAMD-17 total scores and HAMA total scores between the BDDHI group， BDDLI group， UDDHI group， UDDLI group， and the healthy control group（ all P ＜ 0.05）. Post-analysis comparisons revealed that the total scores on the aforementioned scales were higher in all patient groups than those in the healthy control group， with statistically significant differences（ all P ＜ 0.05）. There were statistically significant differences in functional connectivity between the right amygdala-striatal region and the left anterior cerebellar lobe in the four groups（ PFWE=0.001）. Post-analysis comparisons revealed that functional connectivity was higher in the BDDHI， UDDHI， and UDDLI groups than in the healthy control group， and that functional connectivity in the UDDLI group was higher than in the BDDLI group， and these differences were statistically significant（ all P＜0.05）. The sensitivity analysis between non-medicated patients and healthy control group showed that the direction of functional connectivity differences among the four groups was consistent with the results of this analysis. Spearman correlation analysis showed that the functional connectivity between the right amygdala-striatal region and the left anterior cerebellar lobe was significantly negatively correlated with the adjusted HAMD-17 total score in the BDDHI group［ r= -0.539，P=0.003， 95%CI（ -0.792， -0.201）］. In the BDDLI group， there was a significant positive correlation with the total HAMA score［ r=0.515， P=0.005， 95%CI（ 0.141， 0.723）］. Conclusions There are significant differences in the functional connectivity between the right amygdala-striatal region and the left anterior cerebellar lobe in UDD and BDD patients with insomnia of varying severity， and the correlation between this functional connectivity and clinical symptoms varies across different subtypes of BDD.