Aiming at the baseline optimization of phase interferometer direction finding antenna array,the construction of virtual baseline and the optimization of real baseline are presented. Within the physical constraints of the phase interferometer, by reasonably designing the number of virtual baseline and optimizing the ratio of real baseline, the shortcoming of long real baseline caused by non-optimal real baseline ratio in traditional method is overcome, the optimal method of the length of direction finding antenna array baseline under any condition is realized. Finally, the presented method is employed to give the baseline optimization in 0.35~18 GHz, the ambiguity resolution and the angle measurement accuracy are analyzed and verified. Simulation experiment shows that, under the condition of satisfying angle measurement accuracy, the proposed algorithm can optimize the baseline of direction finding antenna array under any condition by optimizing the real baseline ratio.