The stress and deformation characteristics of ultra-deep circular diaphragm wall in soft stratum are complicated and the soil inside the diaphragm wall will produce a soil plugging effect during the excavation process. In this paper,taking the deep foundation pit of well GX12 in Hanjiang-Rongjiang-Lianjiang Drainage system optimization project as a case study,considering the soil plugging effect of the soil in the foundation pit,a three-dimensional numerical model is established,the stress and deformation characteristics of ultra-deep circular diaphragm wall are studied. It is found that the friction force,bending moment,circumferential axial force and horizontal displacement of diaphragm wall increase with the increase of excavation depth;the soil inside the foundation pit forms a soil plug in the diaphragm wall to provide friction resistance to the inner face;the circular diaphragm wall shows flexible characteristics along the depth;the diaphragm wall shows extrusion deformation to the pit,the maximum horizontal displacement is about 0.063%H (H is the excavation depth of the foundation pit);the ground surface around the edge of the diaphragm wall is slightly uplifted during excavation,with the increase of the excavation depth,the surface settlement around the diaphragm wall will appears. The ground surface settlement increases first and then decreases with the increase of the distance from the foundation pit,the maximum value of ground surface settlement is about 0.034%H,and the influence range of surface settlement is 0.57H.