Objective: To compare the anatomic changes of the pelvic floor in women during pregnancy and after childbirth using three-dimensional ultrasound imaging. Methods: Select 80 cases singletons primiparaes at the time of pregnancy and after childbirth in regular prenatal examination in obstetrics and gynecology of our hospital between January 2013 and June 2016. Perineum of three groups was examined using three-dimensional volume transducer at the resting state and state of Valsalva (breathless after deep inspiration). Observe its morphology and internal structure, and to measure the size and area of pelvic diaphragm hiatus of the three-dimensional ultrasonic tomograms, then compare their differences and correlation. Results: (1) Through observing the pelvic hiatus morphology of women in late pregnancy and delivery by the three-dimensional ultrasound, it is shown that the pelvic hiatus morphology was “rhombic” column crack-like structure at about 58.75% in late pregnancy, and “kind oval” at about 51.25% after delivery. Then observing the pelvic hiatus morphology of them in the resting and tension state, the shape variation and the size of the area was found to be increased in tension period then in the resting state. Conclusions：The variation of the pelvic floor structure of postpartum women can be observed dynamically by the perineum 3D ultrasound, and the late pregnancy women and after childbirth who will be significantly increases of pelvic diaphragm, which also proved reliable imaging references for clinic to predict of FPFD after delivery women.