A layout decomposition method, applicable to a double pattern lithography, includes the steps of: putting at least a stitch on each of a plurality of sub-patterns of an initial layout pattern at preset intervals to thereby divide the each of the plurality of sub-patterns into a plurality of unit blocks each selectively labeled as a first region or a second region such that the first region and the second region in same said sub-pattern alternate, wherein any two neighboring ones of said unit blocks attributed to any two neighboring ones of said sub-patterns, respectively, are labeled as the first region and the second region, respectively; reducing the stitches of any two neighboring ones of said unit blocks attributed to any two neighboring ones of said sub-patterns, respectively, so as to generate a first layout pattern having a minimum number of stitches; and reducing the stitches of any two contiguous ones of said unit blocks of each of said sub-patterns in the first layout pattern, so as to generate a second layout pattern having a minimum number of stitches.