The phase center of each element antenna is not necessarily to be determined accurately for beam forming of planar phased-array antenna, but it is necessary for that of non-planar phased-array antenna, or phase is not set correctly and antenna performance is decreasing. In this paper, a new method of computing the element antenna phase center is proposed, and the element antenna phase center of a certain alternating - direction communication antenna is computed, and the effect of element antenna phase center on beam forming of non-planar phased-array antenna is studied. The simulation results demonstrate the effectiveness of the new method.