A biomechanical model of the female pelvic support system was developed to explore the contribution of pelvic floor muscle defect to the development of stress urinary incontinence (SUI). From a pool of 135 patients, clinical data of 26 patients with pelvic muscular defect were used in modelling. The model was employed to estimate the parameters that describe the stiffness properties of the vaginal wall and ligament tissues for individual patients. The parameters were then implemented into the model to evaluate for each patient the impact of pelvic muscular defect on the vaginal apex support and the bladder neck support, a factor that relates to the onset of SUI. For the modelling analysis, the compromise of pelvic muscular support was demonstrated to contribute to vaginal apex prolapse and bladder neck prolapse, a condition commonly seen in SUI patients, while simulated conditions of restored muscular support were shown to help re-establish both vaginal apex and bladder neck supports. The findings illustrate the significance of pelvic muscle strength to vaginal support and urinary continence; therefore, the clinical recommendation of pelvic muscle strengthening, such as Kegel exercises, has been shown to be an effective treatment for patients with SUI symptoms.