Abstract: Objective To investigate the effect of supine hypotension syndrome on pregnancy outcome of puerperas with cesarean section. Methods Totally 94 puerperas with cesarean section were divided into observation group and control group according to hypotension or not, with 47 cases in each group. The systolic blood pressure of the control group was greater than or equal to 100 mmHg, while that of the observation group was less than 100 mmHg. The blood gas indexes were observed in both groups, including alkali residue(BE), arterial hydrogen ion concentration index(pH), partial pressure of arterial oxygen ［p_a(O₂)］, partial pressure of arterial blood carbon dioxide ［p_a(CO₂)］. Blood pressure during delivery and Apgar score of newborns were compared between the two groups. The changes of blood gas indexes of umbilical artery, umbilical vein blood and the abnormal rate of umbilical artery pH were compared between the two groups. Results There were no significant differences in blood gas indexes such as BE, pH, p_a(O₂)and p_a(CO₂)in puerperas between the two groups(P>0.05). There were no significant differences in systolic blood pressure at fetal birth and neonatal Apgar score between the two groups(P>0.05). The lowest systolic pressure before fetal birth in the observation group was significantly lower than that in the control group(P<0.05). There were significant differences in BE, pH, p_a(O₂)and p_a(CO₂)of umbilical vein and artery blood in newborns between the two groups(P<0.05). The abnormal rate of umbilical artery pH≥7.20 in the observation group was significantly lower than that in the control group, and the abnormal rate of pH value ranged - from 7.10 to less than 7.20 was significantly higher than that in the control group(P<0.05). Conclusion Supine hypotension syndrome during cesarean section may lead to hypercapnia and hypoxia in newborns. Active measures should be taken to improve the maternal and infant outcomes.