Objective To explore the value of Z-score in evaluating the distensibility of levator hiatus.Methods A total of 202 women excluding pelvic organ prolapse（POP）were selected as the control group.The parameters of levator hiatus (anterior–posterior diameter, coronal diameter and area) achieved by three-dimensional ultrasound at rest were used as the independent variable and the parameters on Valsalva were used as the dependent variable for linear regression analysis.Z-score model was established according to the parameter determined by regression analysis.The parameters of 259 women with POP（POP group）on Valsalva were imported into the Z-score model to evaluate the distensibility of levator hiatus.ROC curve analysis was used to test the statistical value of Z-score model.Results The regression analysis revealed a good correlation between the area of levator hiatus at rest and on Valsalva（r=0.74）.The z-score model was established with the parameter of levator hiatus area:Z score = (actual observed value -17.37) /3.00.The z-score value of the POP group was larger than that of the control group,and increased with the degree of POP.The difference between groups was statistically significant (P < 0.05).ROC curve analysis confirmed the value of Z-score in detecting abnormal levator hiatus distensibility.For POP grade Ⅱ,z-score value of 0.86 cut-off resulted in sensitivity of 0.90 and specificity of 0.80. For POP grade Ⅲ, z-score value of 1.83 cut-off resulted in sensitivity of 0.89 and specificity of 0.96.Conclusion Z-score can be used to evaluate the distensibility pf levator hiatus scientifically and quantitatively，and when Z-score ≥0.86，it can be diagnosed as abnormal levator hiatus distensibility.