The present disclosure describes an OPC method of preparing data for forming a mask. The method includes setting a plurality of dissection points at the main feature and further includes setting a target point at the main feature. The method includes arranging the two dissection points crossing the main feature symmetrically each other. The method includes separating two adjacent dissection points at one side of the main feature by a maximum resolution of the mask writer. The method includes dividing the main feature into a plurality of segments using the dissection points. The method includes performing an OPC convergence simulation to a target point. The method includes correcting the segments belonging to an ambit of the target point and further includes correcting the segment shared by two ambits.