Objective To observe the image features of pelvic floor structure changes in neonates by four-dimensional ultrasonography and different modes of delivery.Methods Data were collected from the patients in our hospital between May, 2016 to December, 2016. Maternal newborns were divided into three groups according to birth weight and delivery mode: the neonatal spontaneous delivery group (40 cases), giant newborn cesarean section group (55 cases) and the control groups of 150 cases of normal birth weight neonatal spontaneous delivery group or 150 cases of normal weight newborn cesarean section group (all primipara, 42 days postpartum). All the patients were underwent pelvic floor ultrasound examination to observe and record the rest, Anorectal and Valsalva action of three tense bladder neck, cervix, rectal anal canal morphology and activity. Four-dimensional images were reconstructed to observe the shape and continuity of the levator ani muscle at three time points. The area of the levator ani muscle was measured, and the results of ultrasonography were recorded and analyzed statistically.Results There were significant increases in bladder neck mobility and the levator ani muscle rapture in the three groups. The incidence of uterine prolapse was also increased, while the incidence of rectal prolapse and the incidence of rectal prolapse were significantly higher than those of the normal neonates in natural childbirth Valsalva state of the bladder horn, bladder neck tilt angle and bladder neck rotation angle were not statistically significant difference. The caesarean section of the huge neonatal and caesarean section of the normal weight of newborns compared only bladder neck mobility and bladder neck rotation angle increased, the remaining indicators were not statistically significant. There were no significant differences in the incidence of posterior horn and rectum prolapse in the Valsalva state between the neonatal natural labor group and the cesarean section group.Conclusion Compared with the normal weight neonates, the neonatal group had a more obvious effect on the pelvic floor structure of the newborns, especially the huge neonatal group with spontaneous delivery.