Based on the analysis of matrix theory and optimal permissible solution set

a phase perturbation calculating method in phase-only nulling arrays-MDLS method （the Modified Damped Least Square method）is firstly presented

which can be used to solve both the small and the large phase perturbation problems

accurately

efficiently and stably. calculation examples of a sinc pettern array and Taylor pattern array are then given. Finally

the phase variations of different elements are studied. It is shown that the last couple elements are the key elements. This conclusion offers reference to element selection in partial adaptive phase nulling arrays.