Abstract: ob＜x＞jective To investigate the relationship between serum sFlt-1 and t C1q and C5a levels and perinatal outcomes in severe preeclampsia at different onset times. Methods A total of 60 pregnant women with severe preeclampsia who were admitted and delivered in the obstetrics department of Affiliated Hospital of Xuzhou Medical University from February 2019 to January 2020 were selected as the study group, including 30 cases with early onset and 30 cases with late onset of severe preeclampsia respectively. Blood samples were collected on admission without drug treatment.30 normal pregnant women who underwent antenatal examination and delivered at term at the obstetrical department of our hospital during the same period were used as the control group. Blood samples were collected at 34 weeks before pregnancy and at the time of delivery.Perinatal outcomes were recorded in all groups.Serum sFlt-1, complement C1q and C5a levels in pregnant women in each group were detected by ELISA, and the differences of serum sFlt-1, complement C1q and C5a levels in pregnant women in each group and their perinatal outcomes were compared. The correlation between serum indicator levels and perinatal outcomes was analyzed to explore its clinical significance. Results (1) Compared with the control group, serum sFlt-1 and C5a levels in the study group were significantly increased, while serum C1q levels were significantly decreased, with statistically significant differences (P<0.05). (2) Serum LEVELS of sFlt-1 and C5a were increased in women with early onset of severe preeclampsia, while serum levels of C1q were decreased in women with late onset of severe preeclampsia, with statistically significant differences (P<0.05). (3) Serum levels of sFlt-1 and C5a were positively correlated with the incidence of fetal adverse outcomes in pregnant women with severe preeclampsia, while serum levels of C1q were negatively correlated with the incidence of fetal adverse outcomes, with statistically significant differences (P<0.05). Conclusion In severe preeclampsia women, C5a level was significantly higher serum sFlt-1 ex＜x＞pression, however the level of serum C1q lower ex＜x＞pression, its severity level change with preeclampsia and fetal adverse outcomes have obvious relevance, the complement system appears abnormal activation may be associated with the onset of severe preeclampsia, three kinds of joint monitoring is expected to be as important clinical reference indicators