In a charged particle beam drawing data preparing method of preparing drawing pattern data used in a charged particle beam drawing apparatus that forms a micropattern with a charged particle by converting CAD data, it is verified by using interlayer calculation whether a difference exists between the CAD data and the drawing pattern data. When it is verified that a difference exists between the CAD data and the drawing apparatus pattern data, drawing pattern data that compensates for this difference is generated by using interlayer calculation.