A method for preparing a semiconductor structure includes the following steps: providing a substrate including a first region and a second region defined thereon, forming a first mask structure over the substrate, forming a plurality of first features in the first mask structure in the first region, forming a second mask structure over the first mask structure, simultaneously forming a plurality of second features in the second mask structure in the second region and a plurality of third features in the second mask structure in the first region, and transferring the second features and the third features to the first mask structure to simultaneously form a plurality of islanding features in the first region and a plurality of line features in the second region.