Abstract: An alloy layer with special properties will be formed on the surfaces of casts when some kinds of spray alloy powder (nickel-base, ferrite-base, copper-base, etc.) are appled to the surfaces by coat-cast technology. Results of metallogragh, electron microscope and energy spectrum analyses show that the bonding of alloy layer and base metal is of metallurgical union. The bond zone is broad and of jigsaw pattern. The various elements diffuse in one another and the properties of the coat layer are similar to those of the alloy powder. The application of spray weld alloy powder in coat-cast technology solves the problem of alloying surfaces of complicated or small workpieces and leads to economization, particularly for new products.