In a single detector compound axis system, the target will be out of field when the principal axis is in an open-loop state and the controlling for input is not proper after starting auxiliary axis tracking. In order to avoid this situation, it is necessary to feedback the accurate position of piezoelectric ceramics (PZT) to the principle axis. When the PZT mirror is used independently in an open-loop system, the tilt angle of the PZT mirror cannot be controlled precisely. However, the control accuracy of the system can be greatly improved combined with detection and compensation systems. The detection of target position plays a significant role for mirror controlling, which can provide precise control information for servo system in open-loop state, so that it can ensure the target stay at the center of the optical axis. According to the physical structure characteristics of PZT mirror, the position detecting method for mirror in the single detector compound axis system is studied. The principle of the circuit design is present, and a new calibration method with optical autocollimator is proposed. The control formulas are given, and several repeating experiments are accomplished to verify these control formulas. The results show that the error can be controlled within 20 μrad. The study provides foundation for the design of the control system of single detector compound axis.