A method of manufacturing a lithographic mask includes performing optical proximity correction (OPC) for correcting an optical proximity effect (OPE) on a design layout, and forming a lithographic mask based on the design layout corrected by performing the OPC, wherein performing the OPC includes generating a plurality of segments. and adjusting a bias of the plurality of segments, and the plurality of dissection positions include global uniform dissection positions defined for each third length based on a global coordinate system that is a coordinate system of the whole design layout.