Abstract: Provided are a method for manufacturing a metal block which has a complex shape and can maintain a firm sealed unit even when it is repeatedly assembled and the metal block according thereto. To achieve the objective, the present disclosure performs a first electrolytic polishing of the metal block made of stainless steel having a chromium oxide layer, forms an ion-nitrided layer by carrying out an ion-nitriding process, performs a second electrolytic polishing to efficiently remove part of the ion-nitrided layer and induces complex diffusion of high-concentration surface N and C in order to surface-harden a surface layer having a precipitate phase. Accordingly, the present disclosure can increase hardness of the sealed unit inside the metal block up to Hv 400 or more with its corrosion resistance kept, thereby effectively sealing metal.