A mask, a mask assembly, an exposure machine, a method for testing shadowing effect on a window, and a photolithography method are provided. The mask includes a light transmission area; a functional window provided at a side of the light transmission area; and at least one of a first detection mark and a second detection mark; wherein the first detection mark is flushed with a border of the functional window adjacent to an interior of the mask; and the second detection mark is disposed between the profile of the light transmission area and the functional window.