Objective: To investigate the predictive value of Down’s screening serum markers in the middle of pregnancy on preeclampsia (PE) and analyze the correlation between the markers and the outcome of pregnancy. Methods: The data of 70 pregnant women with preeclampsia (39 with mild preeclampsia and 31 with severe preeclampsia) and 50 healthy pregnant women were retrospectively analyzed. In the second trimester of pregnancy (15–19 weeks), all patients received Down’s screening. The levels of serum alpha fetoprotein (AFP), β-human chorionic gonadotropin (β-hCG) and unconjugated estriol (uEs) were compared. Results: There were significant differences in serum AFP, β-hCG and uEs levels among different groups (P<0.05). The serum β-hCG levels of mild and severe PE groups were higher than those of the healthy group, but AFP and uEs levels of the two groups were lower than those of the healthy group (P<0.05), and the β-hCG level of mild PE group was lower than that of the severe PE group (P<0.05). The predicted area under the ROC curve (AUC) of serum AFP, β-hCG, uEs and the combination of them were 0.685, 0.670, 0.669 and 0.712, respectively. There were significant differences in gestational weeks, birth weight and 1 min Apgar score among different groups (P<0.05). The above pregnancy outcome indexes in mild and the severe PE groups were lower than those in the healthy group (P<0.05). The number of weeks of delivery and birth weight in the severe PE group were lower than those in the mild PE group (P<0.05). Serum AFP was positively correlated with delivery weeks and birth weight (P<0.05), while β-hCG was negatively correlated with Apgar score at 1 min after delivery (P<0.05), and uEs was negatively correlated with delivery weeks (P<0.05). Conclusion: The combined detection of AFP, β-hCG and uEs by the Down’s screening in the second trimester of pregnancy has a good predictive value for PE, and has a certain correlation with pregnancy outcome, and the detection value is significant.