Abstract: Aiming at extracting the image of diseased spots and calculating the feature parameters of diseased spots, the present paper studied the extracting method of soybean diseased spots, which used computer digital image processing and genetic algorithm. First, the authors obtained the image, and then recognized the diseased spots through genetic algorithm. At last, the feature parameters of diseased spots were calculated by using the technology of digital image processing. The results indicate that this method can extract the image of diseased spots efficaciously and calculate the feature parameter accurately, which can provide the foundation for recognition of disease category in advance.