Image segmentation and target aspect estimation are very useful for automatic target recognition in SAR imagery. Based on the MRF model, we first segment the image using ICM algorithm. According to the MAP criteria, the image is segmented into target, shadow and background. Then the target pixel closest to the sensor is obtained, and we can get the primary edge and estimate the target aspect angle based on it. These algorithms are applied to SAR imagery from the MSTAR datasets, and the result is better than by other algorithms.