Based on the characteristics of sucrose-crystallizing images in the sugar-boiling process, this paper uses a method called color space conversion which changes the images from RGB color space into HIS color space，and makes use of the relative independence of every component in the HIS color space and the color difference between crystal particles and syrup solution to segment the H component with the improved Otsu’s thresholding method. Many ways are used in the subsequent processing, such as mathematical morphology opening operation, median filter, holes filled, noise removing process of particles in the subsequent processing. Finally, the identification of sucrose-crystallizing particles in the process of boiling sugar is made by analysing the feature value such as the number, size, perimeter, shape index and the area ratio of the crystalline particles extracted from the processed images. Experiments show that this method is effective and practical.