Objective To investigate the role and mechanism of circRNA BRAF_2 in proliferation and apoptosis of placental trophoblast cells in preeclampsia (PE). Methods Placental tissues of pregnant women with normal pregnancy and PE were collected (n=21) in the General Hospital of Ningxia Medical University from January 2018 to February 2019. The expression level of circRNA BRAF_2 in placental tissues of the two groups was detected by qRT-PCR, and the correlation between circRNA BRAF_2 expression level and blood pressure was analyzed. Human placental trophoblast cell lines (HTR8-S/Vneo) were cultured in vitro, (1) Cells were divided into control group and hypoxia group, and the expression of circRNA BRAF_2 were detected by qRT-PCR. (2) HTR8-S/Vneo was transfected with circRNA BRAF_2 lentivirus empty vector and circRNA BRAF_2 overexpression lentivirus, and then divided into control group, circRNA BRAF_2 negative control group and circRNA BRAF_2 overexpression group. The overexpression of circRNA BRAF 2 was verified with qRT-PCR. (3) Based on the successful transfection of circRNA BRAF_2 overexpressing lentivirus, the cells were divided into control group, circRNA BRAF_2 negative control group, circRNA BRAF_2 overexpression group, hypoxia group, hypoxia +circRNA BRAF_2 negative control group, and hypoxia +circRNA BRAF_2 overexpression group. EdU and CCK-8 methods were used to detect the proliferation. Flow cytometry was used to detect the changes of apoptosis level. Western blotting was used to detect the expression levels of apoptosis-related proteins caspase-3, caspase-9,Bcl-2 and Bax. qRT-PCR was used to detect the expression levels of circRNA BRAF_2 in HTR8-S/Vneo cytoplasm and nucleus.Bioinformatics analysis was performed to screen out the miRNA that might bind circRNA BRAF_2 and detect their expression levels in tissues and cells. Results Compared with normal pregnancy group, the expression level of circRNA BRAF_2 was significantly decreased in placenta of PE group (P<0.001), and of circRNA BRAF_2 was negatively correlated with systolic pressure and diastolic pressure (r=-0.4531, P<0.01; r=-0.4381, P<0.01). qRT-PCR showed that compared with control group, the expression level of circRNA BRAF_2 in hypoxia group was significantly decreased (P<0.01), and the relative expression level of circRNA BRAF_2 in negative control group showed no significant difference when ompared with control group (P>0.05). Compared with that in circRNA BRAF_2 negative control group, the circRNA BRAF_2 expression level increased significantly in circRNA BRAF_2 overexpression group (P<0.001). The detection results of EdU and CCK-8 showed that, compared with control group, the percentage of positive EdU cells decreased significantly (P<0.001) in hypoxia group, trophoblast proliferation ability decreased (P<0.001); Compared with the hypoxia +circRNA BRAF_2 negative control group, the percentage of EdU positive trophoblast cells increased significantly in hypoxia +circRNA BRAF_2 overexpression group (P<0.001), and the proliferation ability of trophoblast cells was significantly enhanced (P<0.001). The detection results of flow cytometry showed that, compared with control group, the apoptosis rate of hypoxia group increased obviously (P<0.001); Compared with the hypoxia +circRNA BRAF_2 negative control group, the apoptosis rate of the hypoxia + circRNA BRAF_2 overexpression group decreased significantly (P<0.001). Western blotting showed that compared with control group, the relative expressions of caspase-3, caspase-9 and Bax proteins increased (P<0.01 or P<0.001), and of Bcl-2 protein decreased (P<0.01) in hypoxia group; Compared with the hypoxia + circRNA BRAF_2 negative control group, the relative expressions of caspase-3, caspase-9 and Bax proteins decreased (P<0.001 or P<0.01), and of Bcl-2 protein increased (P<0.05) in hypoxia + circRNA BRAF_2 overexpression group. The results of qRT-PCR showed that circRNA BRAF_2 was expressed mainly in cytoplasm, and bioinformatics analysis showed that binding sites existed between circRNA BRAF_2 and miR-7855-5p. and miR-7855-5p was highly expressed in PE placental tissue than that in normal pregnancy group (P<0.05); Compared with control group, miR-7855-5p was obviously highly expressed in hypoxia group (P<0.001). Conclusion circRNA BRAF_2 can promote proliferation and inhibit apoptosis of PE placental trophoblast cells, and the mechanism may be related to miR-7855-5p.