In a charged particle beam writing method according to one embodiment, a deflector is caused to deflect a charged particle beam and a pattern is written by irradiating a substrate with the charged particle beam. The charged particle beam writing method includes calculating a charge amount distribution based on a charge amount of a beam irradiation region on the substrate immediately after irradiation with the charged particle beam and a diffusion coefficient for electric charge of the substrate, calculating a position shift distribution of the charged particle beam on the substrate based on the charge amount distribution, and correcting an irradiation position of the charged particle beam based on the position shift distribution.