The invention provides a semiconductor structure, a self-supporting gallium nitride layer and preparation methods thereof. The preparation method of the semiconductor structure comprises the following steps: (1) providing a substrate; (2) forming a superlattice structure decomposed layer on the upper surface of the substrate, wherein the superlattice structure decomposed layer at least comprises gallium element; (3) forming a graphical mask layer on the upper surface of the structure obtained in the step (2); (4) processing the structure obtained in the step (3), so that the superlattice structure decomposed layer is decomposed and reconstructed so as to obtain a decomposed and reconstructed laminate; and (5) forming a buffer layer on the upper surface of the structure obtained in the step (4). When the semiconductor structure prepared in the invention is used for growing gallium nitride, gallium nitride crystal seed layers in the decomposed and reconstructed laminate can be used for providing crystal seeds for subsequent gallium nitride growth, and holes inside the decomposed and reconstructed laminate are beneficial for automatic peeling for the subsequently grown gallium nitride and also can be used for reducing the stress among subsequently grown gallium nitride crystal lattices, so that the growth quality of gallium nitride can be improved.