The invention discloses a multilayer core-shell structured Au@SiO2@Ag@SiO2 nano composite material and a preparation method therefor and belongs to the technical field of preparation of nano composite materials. The method comprises the steps of firstly preparing a Au@SiO2 core-shell structured nano-material, then, sequentially adding ascorbic acid, silver nitrate and sodium hydroxide into the Au@SiO2 core-shell structured nano-material, then, adding an amino silane solution into the Au@SiO2 core-shell structured nano-material, then, adding a sodium silicate solution into the Au@SiO2 core-shell structured nano-material, carrying out room-temperature stirring, then, shifting the mixture in oil bath with 93 DEG C for reaction, finally, stopping heating, and carrying out natural cooling. The nano composite material has the characteristics of high detection sensitivity, strong Raman signal, good reproducibility and high accuracy. According to the preparation method, the nano composite material is mainly prepared by chemical methods, and defects caused by crystal lattice mismatch are reduced through coating different noble metals with ultrathin SiO2 layers, so that Raman signals of target molecules are further strengthened. A Raman probe prepared from the nano composite material is easy to functionalize, so that the range of action of the Raman probe is wide.