The Ge nanocrystals were formed in a SiO2 matrix by the multi-energy ion implantation and subsequent annealing. Utilizing the multienergy ion implantation, the Ge atoms were uniformly introduced in the SiO2 matrix. Transmission electron microscopy (TEM) observation showed that the nanocrystal size was more uniform than the case when the Ge nanocrystals were formed by the other methods, such as the single-energy ion implantation and the magnetron co-sputtering. This is due to the uniformity of the Ge concentration in a SiO2 matrix introduced by the multi-energy ion implantation. In addition, TEM observation and Raman scattering spectra showed that the nanocrystal size varied with the annealing temperature and the implantation dose. The uniformity and the size of the Ge nanocrystals were controlled by the ion implantation energy/dose and the annealing temperature. Auger electron spectra showed that the variation of the nanocrystal size was related to the reduction of the Ge oxide. The reduction of the Ge oxide in the SiO2 matrix might be related to the strengths of the chemical bonds.