BACKGROUND The aim of this study was to compare the consistency differences between ultrasound and MRI detection methods and the reliability between 2 independent observers. MATERIAL AND METHODS Under 2 kinds of states - the resting state and muscle contractions state - intra-class correlation coefficients (ICCs) were calculated and the consistency of 2 diagnostic methods was evaluated by 2 independent observers. We also assessed the interscorer reliability of the 2 observers. RESULTS In terms of the evaluation of biological parameters of the pelvic diaphragm, the consistency of the 2 diagnostic methods was moderate. The ICC of pelvic diaphragm area was 0.55 (95% CI 0.35-0.71), anteroposterior diameter was 0.48 (95% CI 0.28-0.64), and transverse diameter was 0.43 (95% CI 0.25-0.63). The ultrasound detection values of the perineal ultrasound were significantly smaller than those of the MRI. In addition, these differences were increased with the rise of the pelvic diaphragm area. CONCLUSIONS By evaluating the pelvic diaphragm in patients with pelvic organ prolapse in the resting state, it was preliminarily confirmed that the consistency of ultrasound and MRI was only moderate. The comparison of these 2 diagnostic methods under the dynamic muscle contraction state needs to be further explored.