Objective To explore the clinical characteristics and pregnancy outcomes of singleton pregnant women with preeclampsia and with different prenatal body mass index（BMI）， and analyze the relative risk of prenatal BMI as a risk factor for adverse outcomes. Methods A retrospective analysis was conducted on the clinical data of 479 singleton pregnant women with preeclampsia that delivered in Nanfang Hospital from January 2016 to December 2021. They were divided into group A （BMI < 26 kg/m²）， group B （26 ≤ BMI < 28 kg/m²）， group C （28 ≤ BMI < 30 kg/m²）， group D （30 ≤ BMI < 32 kg/m²）， and group E （BMI≥32 kg/m²） according to prenatal BMI. The general situation， pregnancy complications and pregnancy outcomes in each group were compared. Results The proportion of adverse outcomes such as severe preeclampsia， placental abruption， fetal growth restriction， and NICU transfer ratio in group A was increased， and these patients terminated pregnancy earlier. In group E， the proportion of cesarean delivery， gestational diabetes and macrosomia was increased， and there was more blood loss during operation and 24 hours after delivery. Patients of Group C had the lowest proportion of induced abortion or stillbirth. Compared with group C， BMI ≥ 32 kg/m² was a risk factor for gestational diabetes； BMI < 26 kg/m² was a risk factor for placental abruption and fetal growth restriction， while BMI < 26 kg/m² or BMI ≥30 kg/m² was the risk factor for the neonatals′ NICU admission. Conclusion There is correlation between prenatal BMI and adverse pregnancy outcomes in pregnant women with preeclampsia， and the appropriate range of BMI is 26 ~ 30 kg/m².