Abstract: As a new radar technology, coherently combining distributed apertures have attracted extensive research from scholars at home and abroad. In this paper, a coherent combining method of the open-loop calibration architecture is introduced. In this method, the technical idea of amplitude and phase calibration of phased array antenna is introduced into the distributed antenna array, and each unit antenna is understood as a small array element in the phased array antenna, and the initial phase and phase center coordinates of the unit antenna can be accurately measured by setting up a beacon source in the far-field area of the unit antenna. Subsequently, based on the principle of phased array antenna beamforming, distributed antenna array can achieve coherent transmission and reception in any direction. The coherently combining method does not rely on the prior information of the target and has low requirements for SNR of the unit antenna, which can realize the full coherent combination on transmission and reception in distributed radar systems of any scale, and opens up a new path for the further development of radar technology. To validate this method, a demonstration system of X-band distributed antenna array with three transmitters and three receivers is built, the experimental results are highly consistent with the theoretical analysis, which fully demonstrates the feasibility of this method.