The precise location from the perturbanced ring image is an important step for hemispherical imaging and tracking (HIT) system targeting object. Conventional method could not satisfy the HIT system tracking object in real time. According to the feature of geometric symmetry of a circle, a new method of resisting light perturbace is presented. The experimental results show that the measurement error might be no more than 1 pixel for perturbance free images. In the meantime, by the proposed method the measurement error might be no more than 5 pixels for perturbanced images.