The invention provides a preparation method of a germanium nano wire field effect transistor. The method comprises the following steps: 1), providing an SGOI substrate structure; 2), etching an SiGe layer, and forming an SiGe nano wire array; 3), performing germanium condensation on a structure in step 2) to obtain a germanium nano wire array with a surface wrapped by an SiO2 layer; 4), removing the SiO2 layer wrapping the surface of the two ends of a nano wire to expose the two ends of the germanium nano wire; 5), depositing a metal lead wire, a source electrode and a drain electrode on the extension line of the germanium nano wire; and preparing a grid electrode on a silicon substrate; 6), forming an Si3N4 protective layer on the surface of the structure formed in step 5); and 7), removing the Si3N4 protective layer in a nano wire pattern area and a metal electrode pattern area until the germanium nano wire, the source electrode and the drain electrode are exposed latelytely. According to the invention, the germanium nano wire is prepared based on a top-down method, the technical process is simple, the controllability is high, the method is completely compatible with a conventional CMOS process, and the cost is quite low. Therefore, the germanium nano wire field effect transistor and the preparation method are suitable for industrial production.