The foundation for offshore wind turbines is subjected to vertical loading caused by structural weight and horizontal loading and moment due to wind- or wave-induced loading. Furthermore, it sustains torque from rotor blades. Based on the framework of hypoplasticity theory, the available general yield function and plastic potential function, a macro-element model for circular shallow foundations on sands under six-degree-of-freedom combined loading has been developed. In this model, to correctly reproduce the mechanical response of offshore foundations under cyclic loading, the concept of equivalent inter-granular strain is introduced into the relationship of generalized forces as well as its corresponding displacements. The performance of the proposed macro-element model is demonstrated by comparing the model predictions with available experimental data from a series of model tests.