A method for surface treatment of a die-casting die

The present invention is to provide a method for surface treatment that substantially provides no nitride compound layer that causes heat checks and abrasion to a die, while nitride is introduced in large quantities into the die internally, and as a result a die-casting die with excellent heat check resistance and excellent abrasion resistance can be produced. The method comprises a step of a nitriding process for forming on an aesthetic surface of the die-casting die a nitrided layer that includes at least a compound layer composed of a nitrogen compound by introducing gas containing at least ammonia gas to a heating furnace, a step of decomposing the compound by exhausting the ammonia gas from the heating furnace and for introducing ambient gas to the heating furnace, to carry out a thermal process to decompose the nitrogen compound, and a step of processing a shot peening process on the aesthetic surface of the die. The thickness of the compound layer contained in the nitrogen layer that is formed in the step of nitriding process is within the range of from 2[Mu]m to 7[Mu]m.