The surface blackening treatment required for castings is on the rise. Because the castings treated by traditional high temperature alkaline oxidation blackening process have brown red or earthy red appearance, they can not meet the requirements of the manufacturer. The normal temperature blackening process has the advantages of beautiful surface, low cost, no impact on workpiece accuracy, good corrosion resistance and so on, and is welcomed by users. In terms of structure, the inner cavity and shape of the casting parts shall be formed at one time by casting method to make them close to the final shape of the parts, so that the machining and assembly processes can be reduced at least in terms of dimensional accuracy and surface quality, so that the castings can approach the requirements of the products, and achieve yuan margin or small margin; On the other hand, the retained original casting surface is beneficial to maintain the superior performance of corrosion and fatigue resistance of castings, so as to improve the service life of products. It is the future direction to improve the dimensional accuracy and reduce the surface roughness of castings and promote the development of near net shape casting technology.