Multi-focus rock debris images have large numbers of pixels and high resolution. Although Scale Invariant Feature Transform(SIFT) algorithm and Speeded Up Robust Features(SURF) algorithm have met registration accuracy，their time efficiencies are both far less than the real-time requirements. A kind of fast algorithm，directional binary Oriented Brief(ORB) algorithm, is applied to multi-focus rock debris image automatic registration. Experimental results show that proposed method is efficient in registration accuracy, and its speed has been increased significantly as well.