Chromatic aberration would make edge contours of the image become fuzzy when the light source of the size measurement system based on machine vision is chromatic. This paper mainly studied the influence of chromatic aberration on accuracy of size measurement. To acquire images and dimension measurement results of the standard cylinder, a machine vision measurement system was built as a platform and white (chromatic), red, green, blue LED light sources were respectively used with treatment by software. When the light source was chromatic, the repeatability error and the linearity error of measurement were within 1 μ m and 2 μ m; when using monochromatic light as the light source, the repeatability error and the linearity error of measurement were controlled within 0.5 μ m and 1 μ m. The experiment showed that chromatic aberration influenced the repeatability and the linearity accuracy of measurement of machine vision and the monochromatic light can be used to avoid chromatic aberration and to further improve the measurement accuracy.