For studying the technology of the critical dimension measurement using an electron beam (EB), a computer simulation based on the Monte Carlo and the surface charge methods is carried out, and a wave form of backscattered electrons (BE’s), which hardly suffer from the charging phenomenon, is precisely analyzed using this simulation. First, line widths obtained individually by threshold, maximum slope, and linear approximation methods are examined about various incident‐EB conditions such as an accelerating voltage and a beam diameter. The dependencies of pattern structures, such as dimension, side‐wall angle, and materials of the patterns, on measured line width are evaluated next. As a result of these calculations, it is found that the variation of the incident‐EB conditions doesn’t affect practically the results of the line‐width measurement in BE‐detection systems, while secondary‐electron signals are easily deformed by the charging phenomenon. Although the measured width much depends on the pattern structure, the linear approximation method is comparatively suitable for the purpose of obtaining the width of bottom edges in BE‐detection systems.