In this paper, a scheme of small body autonomous optical navigation is presented which takes the opportunity feature region (OFR) as the navigation characteristic, aiming at the requirements of autonomy, real-time and navigation precision for small body exploration mission. The search criterion of the OFR is given after defining the OFR. Then, perform the detection and matching process of OFRs in the sequence images acquired by the navigation camera. Hence, the attitude and position determination of the spacecraft could be obtained employing the normalized 8-point algorithm. Furthermore, the performance of the relative autonomous optical navigation system is analyzed by mathematical simulation, which verifies the effectiveness of the proposed method based on the OFR.