Aiming at the blind spot of on-line fault monitoring of photoelectric tracking equipment, the cable signal transmission fault detection method is studied. In this paper, the cable detection is based on the principle of impedance mismatch at the fault location, and on the basis of the reflection method, a design with strong anti-interference and no communication influence and good correlation with the test signal, using the signal generator and the data acquisition system to inject the signal and collect the reflected signal, and eliminating the cross term caused by the signal superposition of the collected signal, and finally determining the cable fault location and fault type by the correlation analysis of test signal and the collected signal , and obtaining the fault unit of the equipment. Verifying the detection performance, stability and engineering practicability of this method by comparing performance with the spread spectrum time domain reflectance method.