The Global Navigation Satellite System (GNSS) adaptive array suffers from phase distortions owing to beam forming processing which in turn affect the navigation precision. In high precision GNSS applications, the distortions must be evaluated. Traditional phase performance evaluation approach is based on the fixed reception pattern antenna. A new approach to evaluate phase performance of adaptive array is presented. The method takes into account the interfering scenes and the average phase centre variation performance for different adaptive algorithm and array geometry can be obtained.