Abstract: Some footings of ocean engineering structures are always to withstand their own vertical gravity loads and the horizontal loads induced by sea waves and current, which makes the foundation subjected to concentrated force, overturning loads and torque loads. The above loading state including vertical, horizontal and overturning moment loads is termed as combined loading. It is very necessary for the safety of ocean engineering structures to study the ultimate bearing capacity and failure mode of submarine seabed. By use of the finite element analysis software ABAQUS and the elastic-plastic limit equilibrium theory of soils, the ultimate bearing capacity of three-dimensional circular footing with six-degrees-of-freedom is analyzed. Based on the above numerical results, the failure mode and ultimate bearing capacity of seabed under monotonic loading are released, and reasonable failure envelopes for submarine soils under circular footing are given. The present failure mode and failure envelope can be employed to reasonably estimate the bearing capacity of three-dimensional footing under combined loading.