Abstract： Objective To investigate the MRI features of urethral sphincter in female with stress urinary incontinence(SUI) by the study of the indexes of the thickness of middle urethral sphincter, the function urethral length and bladder neck funnel . Methods Forty patients of female patients diagnosed as SUI by clinical were retrospectively as SUI group, and 40 asymptomatic female volunteers were recruited as reference group. All of the subjects were tested by pelvic MRI scanning both in static status and in the condition of Valsalva. The thickness of middle urinary sphincter was measured in the horizontal axis plane. In the midsagittal plane, the function urethral length was measured from the internal orifice to perineal fascia. The bladder neck funnel whether exist was observed from the midsagittal plane. For the comparison of the urinary sphincter thickness and urethral length of the two groups, independent sample t test was adopted. For urethral length in static status and under the condition of Valsalva, paired t test was done. For comparison of positive rate of the bladder neck funnel, Chi?squared test has been done. Results The value of the middle urinary sphincter thickness in the groups of SUI and reference were (2.23±0.68) mm and (2.69± 0.75) mm, respectively. Thus the differences of the two groups had statistical significance (t=-2.839, P<0.01 ). In the static status, the urethral length in SUI and reference group were (2.72±0.51) cm and (2.94± 0.34) cm respectively, wheras in Valsalva condition, the value were (2.33 ± 0.49) cm and (2.43 ± 0.43) cm respectively. The differences of the two groups had statistical significance in static status (t=-2.322, P=0.023), wheras there had no statistical significance in the two groups in Valsalva condition (t=-1.049,P=0.297). For SUI and reference group, both in static status and Valsalva condition, the difference of function&nbsp;urethral length had statistical significance (P< 0.01). The positive rate of bladder neck funnel for SUI was 72.5% (29/40), and for reference was 22.5% (9/40), the difference of the two groups had statistical significance(χ2=20.050, P<0.01). Conclusion For female SUI patients, urinary sphincter muscle is much thinner, function urethral length is much shorter and has higher positive rate of bladder neck funnel.