A mask and an assembling method are provided. The mask includes a plurality of strip-shaped supporting structures; a mask sheet supported by adjacent supporting structures, having a mask pattern; and a frame having an opening area; each of the supporting structures includes an intermediate portion and extension portions at both ends of the supporting structure, a width of the intermediate portion is greater than a width of each of the extension portions; the frame is provided with a groove connected with the opening area; and the extension portions of the supporting structure and an transition area in the intermediate portion close to the extension portion are located in the groove, and a fixing point configured to fix the supporting structure with the groove is at least disposed in the transition area.