A mask plate, a method for manufacturing a color film substrate and a color film substrate for decreasing the segment difference of the color filter layer are disclosed. The mask plate includes a plurality of first regions, each of the plurality of first regions corresponding to each subpixel unit; and a second region between two adjacent first regions. Each first region is respectively provided with one first subregion for forming a color filter layer pattern within an opening region of a black matrix layer, and two second subregions for forming a color filter layer pattern within a non-opening region of the black matrix layer. The first subregion is between the two second subregions. In each second subregion: along the direction away from the first subregion, the transmittance of the second subregion gradually decreases or increases.