The inverted T-type breakwater with jackets and pile foundations which mixes gravity breakwater with pile is a new type of breakwater; its working mechanism and failure pattern are unclear. A 3D elastoplastic finite element model is established for its stability analysis. Based on the displacement field distribution of the structure in a critical state

the instability mode can be concluded as the inverted T-type breakwater with jackets and pile foundations rotates around a point that is below the top structure and deviates the axis of the pile foundations. For the purpose of engineering application

a simplified calculation method for anti-overturning and anti-sliding analyses is presented. In comparison with the finite element method

the simplified calculation method is reliable.