There are many methods of casting magnesium alloys, including gravity casting and die casting, which can be subdivided into sand casting, permanent die casting, semi-permanent die casting, investment casting, squeeze casting, low pressure casting and high pressure casting. Generally speaking, Die Casting refers to high pressure Casting to distinguish gravity Casting from low pressure Casting. For specific materials, the appropriate casting method should be selected according to its chemical composition and technological requirements. The alloy composition and casting process have an important effect on the microstructure. Alloying elements, especially rare earth elements (RE), cause complex changes of mesophore structure, which have great influence on the microstructure and properties of magnesium alloys.