A decoration-used mold unit for defining a border on a work piece to facilitate cutting or milling. The mold unit includes an elongated rectangular main body formed with a first window for processing a first sink and a second window for processing a second sink. A first chucking section protrudes from a first side of the main body. A second chucking section protrudes from a second side of the main body. At least one abutting member is adjustably arranged at the second chucking section. The first chucking section and the abutting member respectively abut against two opposite sides of the work piece to clamp the work piece. In the processing procedure, the blade is restricted within the first and second windows so that the work piece will not be over-milled and the borders of the sinks keep straight.