A layout pattern decomposition method includes following steps. A layout pattern is received. The layout pattern includes a plurality of features, and an edge-to-edge space is respectively defined in between two adjacent features. A sum of a width of the edge-to-edge space and a width of the feature on a left side of the edge-to-edge space and a sum of the width of the edge-to-edge space and a width of the feature on a right side of the edge-to-edge space are respectively calculated. The sums and a predetermined value are respectively compared. When any one of the sums is smaller than the predetermined value, the two features on the two sides of the edge-to-edge space are colored by a first color and alternatively a second color. The features including the first color are assigned to a first pattern and the features including the second color to a second pattern.