The shear mechanism of offshore wind monopile-soil interface plays a key role in its bearing capacity. Large-scale monopile-soil interface shear tests were conducted with typical clayey, sandy, and combined clayey-sandy soil under different cyclic load, in consideration of China’s widely distributed thick mucky clay and complex marine load. The shearing area was 2 400 cm² to avoid the size effect and stress concentration in the boundary. Interface shear stress increases with the increasing of shear displacement to peak strength, and remains stable, proving the inexistence of cementing force. The clayey interface shear strength lower than sandy interface under same condition. Clayey-sandy interface shear strength is between them, mainly controlled by sandy part, and its shear displacement at peak strength is much higher due to coordinate deformation. The interface shear strength grows with normal pressure, but lower than shear strength of soil, making interface the weak part of pile bearing capacity. Cyclic load diminishes interface shear strength, mainly determined by amplitude. The influence of cyclic load is more obvious in clayey interface than sandy interface.