A lithography simulation method includes: taking in design data of a pattern to be formed on a substrate and mask data to prepare a mask pattern used in forming a latent image of the pattern on the substrate by transmission of an energy ray; obtaining the latent image of the pattern by calculation of an intensity of the energy ray; locally changing, at least in a portion corresponding to a pattern of interest, a relative position in a direction of the intensity of the energy ray between a latent image curve and a reference intensity line in accordance with a distance between the pattern of interest and a pattern of a neighboring region , the latent image curve being an intensity distribution curve of the energy ray constituting the latent image, the reference intensity line being defined to specify a position of an edge of the pattern of interest; and calculating a distance between intersections of a portion of the latent image curve corresponding to the pattern of interest and the reference intensity line in the changed relative position to define a line width of interest of the pattern of interest.