A method and system is disclosed for examining mask pattern fidelity. A mask picture is generated from a first mask with a first OPC model applied to a mask design. The mask picture is converted into a mask based simulation file. A first simulation is conducted under a first set of predetermined lithography processing conditions using the converted simulation file to generate one or more files of a first set representing wafer photo resist profile thereof. The first OPC model is applied to the mask design in the database mask file. A second simulation is conducted under the first set of predetermined lithography processing conditions using the OPCed mask design to generate one or more files of a second set representing wafer photo resist profile thereof. The first and second sets of files are evaluated for inspecting mask fidelity.