A charged particle beam writing method includes measuring a topography of a backside of a substrate without an influence of a gravity sag, calculating a first positional deviation amount of a pattern written on a frontside of the substrate in a case of the backside of the substrate having been corrected to be flat, based on the the backside topography of the substrate, calculating a first coefficient of a first approximate expression indicating a positional deviation correction amount for correcting the first positional deviation amount, based on the first positional deviation amount, adding the first coefficient to a second coefficient of a second approximate expression indicating a positional deviation correction amount for correcting a second positional deviation amount of the pattern written on the frontside of the substrate in a case of the backside of the substrate having not been corrected to be flat, and writing the pattern on the frontside of the substrate utilizing a charged particle beam, based on one of a positional deviation correction amount obtained by a third approximate expression indicating a positional deviation correction amount using a third coefficient obtained as a result of the adding, and the positional deviation correction obtained by the second approximate expression.