Objective To simulate the biomechanical characteristics of pelvic-ligament-muscle during vaginal delivery and rest, and to explore the injury of levator ani muscles during vaginal delivery, pelvic organ prolapse and stress urinary incontinence. Methods The three-dimensional (3D) nonlinear finite element model of pelvis-ligament-muscle was established to calculate the stress and strain distributions and injury of levator ani muscles under different abdominal pressures and loads. The stress and strain distributions as well as damage of type I, Ⅱ, Ⅲ stress urinary incontinence and pelvic organ prolapse were also calculated. Results The highest equivalent stresses of levator ani were 14, 29, 43, 86, 144, 230 kPa, respectively, when the abdominal pressure was 1 kPa under the load of 3, 5, 8 kPa and the abdominal pressure was 1.5 kPa under the load of 3, 5, 8 kPa. The stresses of type I, Ⅱ, Ⅲ stress urinary incontinence and pelvic organ prolapse were 1.69, 1.01, 0.70, 1.58 MPa. Conclusions Vaginal delivery would result in the damage to the puborectalis and the middle of the pubococcipital muscle, which was consistent with the damage of the anal levator muscle with pelvic floor dysfunction. This study uses scientific method to find out the exact location of pelvic floor injury during vaginal delivery, which can provide references for clinicians to prevent pelvic floor disease and formulate post natal rehabilitation training.