Lubrication mechanism of emulsion coating for die-casting die can be as sumed that a large portion of the lubricants has been thermo-decomposed into gaseous state to form consistent and proper gas-gap between die and liquid metal during die-casting process. Because lubricant layer consists of released gas and residual lubricant, the evolved gas features and friction coefficient of the lubricant at high temperature are the key factors controlling emulsion die-coating. Friction coefficient at high temperature plays an important role for die-casting in the beginning of process, and then gaseous lubrication controls the whole die casting process. It is necessary to add high heat resistant component to the coating to ensure consistent and stable release of the gas in the whole process for large aluminum alloy and Mg alloy casting.