A multi charged particle beam writing method includes calculating first shot positions of multiple beams, each of which includes a distortion amount of an irradiating corresponding beam, in a case of irradiating each beam, based on control grid intervals, calculating first condition positions based on a pre-set condition, each of which is arranged in a corresponding first region surrounded by closest second shot positions of 2×2 in length and width of the first shot positions, calculating, for each of second regions respectively surrounded by closest second condition positions of the first condition positions, an area density of a figure pattern in overlapping with a second region concerned, calculating an irradiation amount or an irradiation time of each beam whose corresponding first shot position is in a corresponding second region, based on an area density, and writing a pattern by irradiating a beam of the calculated irradiation amount or time.