Objective To study the closure time of neonatal ductus venosus and the Z score regression equation, and to explore the variation of closure time of neonatal ductus venosus with gestationalage.Methods Color doppler ultrasound was applied to detect the closure time of neonatal ductus venosus in normal newborns, Z score regression equation ( lnY =a +bX +cX2 ) for the closure time of neonatal ductus venosus ( Y ) was developed by regression analysis which used gestational age ( X) as an independent variable. The Z scores of the closure time of neonatal ductus venosus in different gestational age were calculated by the formula [ Z = ( M - Y )/S x , M for observation value, Y for predictivevalue].Results There were 432 cases in our study.The closure time of neonatal ductus venosus was negatively related to gestational age ( r = -0. 938 , P <0. 001 ) . The nonlinear regression equation was lnY= -5. 228+0. 089X-0. 000228X2, R2 =0. 854, Sx =0. 214(P<0. 001). Based on the predicted mean of the closure time and Sx related to different gestational age, Z scores for specific closure time of neonatal ductus venosus could be calculated by the formula [ Z =( M -Y)/Sx ] . The Z scores were normally distributed,and did not change with gestational age.Conclusions Theclosure & nbsp;time of neonatal ductus venosus is negatively related to gestational age. The Z scores obtained by the predicted nonlinear regression equation are normally distributed.