Considering the plate quality detection method in accordance with machine vision, an innovative dot area coverage percentage measurement method for plate microscopic image based on color segmentation was proposed. Plate microscopic image was acquired firstly by using image capture device, then the plate microscopic image was transformed from RGB to HSI space. The plate microscopic image was segmented from coarse to fine according to the saturation and the hue information. After morphological denoising, the dot area coverage percentage was calculated by the pixel statistical method. The experiment showed the dot area coverage percentage measurement method based on color segmentation was of high measurement precision and good plate applicability.