The invention provides a method for preparing SGOI or GOI by utilizing a C adulteration SiGe preparing layer. The method comprises the first step of forming the C adulteration SiGe preparing layer on the surface of a top silicon layer of SOI, the second step of forming an SiGe material layer on the surface of the C adulteration SiGe preparing layer, the third step of forming an Si cap layer on the surface of the SiGe material layer, the fourth step of oxidizing annealing the structure to oxidize the Si cap layer and gradually oxidize the SiGe material layer, the C adulteration SiGe preparing layer and the top silicon layer to enable Ge in the SiGe material layer and the C adulteration SiGe preparing layer be diffused to the top silicon layer and gradually concentrated and forming a top SiGe layer or a top Ge layer and an SiO2 layer on the upward side, and the fifth step of removing the SiO2 layer. Lattice mismatch between the SOI top silicon layer and the epitaxial SiGe material layer is reduced through the C adulteration SiGe preparing layer, and accordingly defects produced in the process of concentration are reduced. The prepared SGOI has the advantages of being high in relaxation, low in defect density, high in Ge component and the like.