Accurate evaluation of the vertical bearing capacity of the mat foundation on the clay seabed is of great significance for the safe operation of the mat-supported jack-up platform in the marine environment. Combining the centrifuge test and the coupled Eulerian-Lagrangin (CEL) large deformation numerical calculation method, the vertical bearing characteristics of mat foundation on horizontal and sloping clay seabed were studied. First, the distribution law of undrained shear strength of soil along the depth was obtained through the T-bar penetration test. Then, the vertical bearing characteristics of two kinds of bottom mat foundations on soft clay seabed were tested. Finally, the vertical bearing characteristics of the mat foundation were discussed in combination with the numerical method of CEL large deformation, and the bearing capacity and soil displacement changes of the foundation on different inclination seabed were analyzed. The results show that the foundation load displacement curve has no obvious peak value, and the bearing capacity of the square foundation is slightly higher than that of the rectangular foundation. The development law of soil excess pore pressure is basically consistent with the change law of bearing capacity in the process of foundation entering the sea bead, and most of the vertical stress is borne by the excess pore pressure. The foundation bearing capacity gradually decreases as the slope of the seabed increases, and the soil below the foundation tends to slip in the direction of the slope angle, which may lead to slip damage of the seabed. Therefore, operation in the seabed area with a large slope should be avoided in actual practice.