Objective To investigate the evaluation value of morphological changes of mitral valve device after left atrial appendage occlusion by transesophageal 3D echocardiography to provide more reference for the selection of preoperative occluder. Methods 35 patients with atrial fibrillation treated by left atrial aural occlusion were retrospectively chosen in the period from January 2017 to December 2022 in our hospital. 2D/3D transesophageal echocardiography was performed before and after surgery. The change of quantitative parameters related to the mitral valve device was analyzed to further evaluate the correlation between the compression ratio of the occlusive device and the quantitative parameters related to the mitral valve device. Results The anterolateral to posterolateral mitral annulus, the three-dimensional annulus circumference, the two-dimensional annulus area, the three-dimensional annulus area, the dome volume, the projection area under the dome and the diameter at the joint of the mitral annulus after surgery were significantly smaller than before surgery(P<0.05). The anteroposterior diameter/anterolateral to posteromedial diameter after surgery was significantly larger than before surgery(P<0.05). There was the significant positive correlation between flap dome volume and occluder compression ratio(P<0.05). There was no significant correlation between the compression ratio of the occluder and other quantitative parameters of the mitral valve device(P>0.05). Conclusion Transesophageal 3D echocardiography can be used to accurately evaluate the morphological changes of the mitral valve device after left atrial appendage occlusion and both the volume of the fornix before the mitral valve device and the compression ratio of the occlusive device can affect the occlusive device.