A method of preparing mask data, the method begins with performing a logic operation to a design layout, and an optical proximity correction (OPC) is performed to the design layout to form an OPC feature. The OPC feature has a first jog and a second jog on a line, and the first jog is larger than the second jog in width. The OPC feature is resized to form a resized first jog and a resized second jog on the line if a width ratio of the first jog to the second jog being smaller than a predetermined value.