Mg2+-Ge4+ ions substituted YAG: Ce3+ phosphors ((YAl5-2xMgxGexO12)-Al-3: Ce3+) were prepared by high temperature solid state reaction method. X-ray diffraction (XRD), Scanning election microscope (SEM), Photoluminescence (PL) spectra and so on were used to characterize the samples. The effects of Mg2+-Ge4+ concentrations on the morphology, structure, luminescence properties, fluorescence lifetime and white LED performance of YAG: Ce3+ phosphors were studied in detail. The results indicate that Mg2+-Ge4+ ion pairs can partially substitute the Al3+ ions of YAG successfully. With the substitution, the garnet crystal structure remains unchanged. However the emission spectra show a progressive red-shift, from 528 to 552 nm (about 24 nm). The lifetime decreased rapidly from 84 to 26 ns. In particular, the correlated color temperature (CCT) decreases gradually from 6798 to 3261 K and the color rendering index (CRI) increases from 76.5 to 89.3 with the increasing of the incorporation content of Mg2+-Ge4+ ion pairs.