Abstract: Compound axis servomechanism is an engineering realization of the two-channel control system, and is widely used in the optoelectronic tracking control, laser communication and beam control. The tracking precision and control bandwidth are greatly improved by the compound axis servomechanism. In high tracking control system, the compound axis servomechanism is an effective way to obtain the tracking precision of the microradian, even the submicroradian. In this paper, the basic theory and primarily technical problems of the compound axis servomechanism were introduced. In the control system of the compound axis servomechanism, the control bandwidth matching of main and subsystem tracking control was a prerequisite of compound axis servomechanism, and the control performance precision of compound axis servomechanism depended on the closed loop control performance of fast steering mirror. The recent development and technical improvement was analyzed, such as multiple compound axis servomechanism, pseud compound axis servomechanism, adaptive optics, feed forward control and so on in the compound axis servomechanism.