Beam forming processing of adaptive antenna introduces the change of antenna phase center. In order to solve this problem, an evaluation method of adaptive antenna phase center on the basis of available beam was proposed. The method achieved the purpose in three steps: setting the available beam threshold; obtaining phase pattern set in available beam areas when the direction of interference signal distributed uniformly; fitting the phase pattern set to get the average phase center variations of adaptive antenna by using least square method. The method was validated by simulation under four typical four-elements-arrays. The analysis of simulated results indicates that the proposed method can be used to evaluate the phase center characters of adaptive antenna conveniently. What’s more, in order to fulfill the performance of high precision for adaptive antenna array, a choice is to reduce the available beam threshold. The research can be used as a guideline for choice of distributions of antenna elements in high-precision GNSS.