A method for generating a layout pattern includes following steps. A basic layout pattern including a plurality of first stripe patterns in a first cluster region is provided. Each first stripe pattern extends in a first direction, and the first stripe patterns have equal pitches in a second direction. A plurality of anchor bar patterns are generated. Each anchor bar pattern extends in the first direction, and the anchor bar patterns have equal pitches in the second direction. Edges of at least one of the anchor bar patterns in the second direction are aligned with edges of two adjacent first stripe patterns respectively. At least one of the anchor bar patterns overlaps a first space between two adjacent first stripe patterns. At least one first mandrel pattern is generated at the first space overlapped by the anchor bar pattern, and the first mandrel pattern is outputted to a photomask.