Distributed coherent aperture radar(DCAR) is composed of several small aperture radars. Through the distributed coherent processing of multi-node echo, it can be equivalent to large aperture radar, so as to improve the echo SNR and greatly improve the target detection performance, which has important research value. In this paper, aiming at the coherent synthesis of distributed coherent aperture radar, phase adjustment of transmitting signal is carried out online to ensure the phase coherence of echo signal and achieve the coherent synthesis at the target. Firstly, a signal model related to coherent synthesis is established, and then the effect of time delay and phase error on the coherent synthesis is analysed through simulation analysis and measured data processing, which preliminarily verifies that the coherent synthesis performance of the distributed radar system meets the requirements, which is beneficial to the design of the subsequent target relative position and attitude measurement experiment.