Objective:To study the correlation between umbilical artery blood gas (UABG) and Apgar score of neonates and the risk factors of low base excess (BE) in UABG.Methods:From March 2017 to September 2020, newborns without congenital malformation born in three hospitals were prospectively enrolled and received UABG analysis. According to their Apgar score, the infants were assigned into low Apgar score group and normal Apgar score group. According to BE of UABG, they were assigned into BE<-12 mmol/L group and BE≥-12 mmol/L group. The UABG indexes including abnormal pH and BE between the low Apgar score group and the normal Apgar score group were compared. The risk factors of low BE in UABG were analyzed.Results:A total of 1 351 qualified samples were included including 208 cases in low Apgar score group and 1 143 cases in normal Apgar score group. 115 cases were in BE <-12 mmol/L group and 1 236 cases in BE ≥-12 mmol/L group. The incidences of abnormal pH and BE values in the low Apgar score group were higher than the normal Apgar score group [50.0% (104/208) vs. 13.8% (158/1 143), 34.6% (72/208) vs. 3.8% (43/1 143)]. The pH and BE values of UABG were positively correlated with 1 min Apgar score ( r=0.402, 0.398, P<0.001). Multivariate logistic regression analysis indicated that the risk factors for BE<-12 mmol/L were Ⅲ° contaminated amniotic fluid ( OR= 3.155, 95% CI 1.972~5.025, P<0.001) and placental abruption ( OR = 3.968, 95% CI 1.992~7.874, P <0.001). Conclusions:The pH and BE values of neonatal UABG are positively correlated with 1 min Apgar score. Ⅲ° contaminated amniotic fluid and placental abruption are risk factors of low BE in UABG.