Abstract: As the anchoring foundation of the tension leg platform (TLP), the suction caisson foundation is mainly subjected to the vertical pullout loads. The uplift bearing capacity of caisson is only composed of the internal and external frictions and caisson weight under the drainage condition, so the uplift bearing capacity is very small. Therefore, the gravitational reinforced composite suction caisson foundation is proposed to solve this problem. The uplift bearing capacity of the new suction caisson foundation and the shearing characteristics of caisson-cement soil interface are studied through the model tests, large-scale shear tests and push out tests. The test results show that the uplift bearing capacity of the new suction caisson foundation is much higher than that of the traditional suction caisson foundation. It increases gradually with the increase of the additional load and reinforcement range. The interface shear strength of caisson-cement soil increases with the increase of normal stress and cement ratio. When the rib width is wider, the area of the shear zone above the ring rib is larger and the ratio of the relative area is larger, the shear strength of the whole interface between the caisson and cement soil is higher. Based on the uplift bearing characteristics of new caisson by model tests and push out tests, the interface failure mode, the overall shear strength, the bearing capacity composition and the relevant method are proposed for analyzing the uplift bearing capacity of suction caisson foundations. It can provide a reference for the engineering design of the new suction caisson foundation under vertical loads.