Abstract: As the permanent support seabed structures for subsea wells,pipeline manifolds and pipeline terminations,the mudmat foundations have obviously complex,nonlinear and uncertain loading,which makes the research of mudmat foundations' stability a big challenge. In this paper,the bearing capacity of mudmat foundations in rectangular,square,hexagon and circle are researched under the same steel quantity condition on the deep clay where the strength increases linearly with depth. Numerical simulation method is utilized to investigate the failure envelops and formulas of mudmat are established in V-H、V-M、V-T、H_x-H_y、M_x-M_y、T-H & T-M load space,when combined vertical load V,Horizontal load H,moment load M,and torque load T were applied Analysis results show that the shape of mudmat has great influence on its bearing capacity. Concretely,the circular mudmat is suitable on the condition of large V load,while the rectangular and square mudmat is better when the H is obvious among all the loads. When M is the control load,different shapes of the mudmat meet different conditions separately. But the rectangular or the square mudmat is optimal and the hexagon or the circle mudmat take second place when the influence of T load cannot be ignored.