Abstract: In distributed aperture coherent radar system, the signals transmitted by all base unit radars should be made to arrive at target with the same phase to achieve the coherent transmit mode. Therefore, the phase difference between any two transmitted signals at the target was needed to track, and then the estimated value was used to compensate the transmit signals to make them in phase at target. According to the working mechanism of distributed aperture coherent radar, two tracking methods of phase difference based on the coherent receive mode and the coherent transmit mode were proposed in this paper, respectively. And then we studied the two methods according to theoretical analysis. It was found that the former method could track the phase difference accurately, while the tracking accuracy of the latter method was affected by the phase synchronization error between two base units of distributed aperture coherent radar. Therefore, a closed-loop tracking technology of phase difference was proposed base on the coherence performance monitoring. At last, simulation results verified the effectiveness of the two proposed tracking methods of phase difference. The research on tracking technology of phase difference for distributed aperture coherent radar is helpful to realize the new radar system.