In this book, we firstly proposed the preparation of alumina powder via nonaqueous precipitation process, and obtained the monodisperse ultrafine alumina powder. It was used to prepare Al2O3@YAG: Ce core-shell yellow phosphor for white LED application. Glacial acetic acid precipitator was firstly used and crystal precipite was obtained, which was the basis for preparing monodisperse ultrafine alumina powder. We finally obtained monodispersed Al2O3@YAG: Ce core-shell yellow phosphor with high-performance. The mechanism of these processes were also illustrated.