The paper presents an approach for medical image categorization based-on Gaussian mixture model in CBMIR system. The medical image categorization is a very complicated problem because the characteristics on texture, shape and intensity among the images of different parts of body are distinct differences. First, we extract the characteristic vectors of the training image set. Then, we choose the optimum features which can distinguish different classes and the same class better. After getting GMM parameters by EM algorithm, we categorize the test images. The experimental results indicate that the method performs well on CT image categorization.