Objective To explore the clinical application value of Down's screening according to the results of Down's screening, and to compare the adverse pregnancy outcomes of different risks of Down's screening. Methods The Down's screening results of 19630 pregnant women in the second trimester (14w-21w + 6) from November 1, 2014 to March 31, 2019 were analyzed retrospectively.The positive rates of high risk and critical risk of three diseases (21-trisomy syndrome, 18-trisomy syndrome, OSB) were counted respectively, and the incidence of adverse pregnancy in the high-risk group, critical risk group and low-risk group were followed up. Results Among 19630 cases of prenatal screening in the second trimester, the positive rate of 21 trisomy high risk was 6.40%, and the positive rate of 21 trisomy critical risk was 14.6%.The high-risk positive rate of 18 trisomy was 0.17%, and the critical risk positive rate of 18 trisomy was 0.28%.The high-risk positive rate of OSB was 1.44%, and the positive rate of 21 trisomy, 18 trisomy and OSB were 77.1%.Follow up and compare the pregnancy outcomes of high-risk group, critical risk group and low-risk group.The incidence of adverse pregnancy in high-risk group was 1.97%, that in critical risk group was 0.72%, and that in low-risk group was 0.The incidence of adverse pregnancy outcomes in the three groups were compared, the difference was statistically significant (P< 0.01).The incidence of adverse pregnancy in the high-risk group was higher than that in the critical risk group, and the incidence of adverse pregnancy in the critical risk group was higher than that in the low-risk group. Conclusion Critical risk pregnant women and high-risk pregnant women should pay attention to the same, critical risk pregnant women need to carry out follow-up ultrasound testing, non-invasive fetal DNA screening, and amniotic fluid cell nuclear type analysis, so as to find birth defects as early as possible.