Abstract: The robustness of beampattern optimization for arbitrary geometry arrays is studied in this paper. Based on the sensitivity analysis of beampattern,the close form formula for sidelobe distortion of beampattern is deduced as a function of array perturbations and weighting vector norm. Using this sidelobe distortion formula,a criterion to select the upper limit of weighting vector norm with required robustness is proposed. The effectiveness of the proposed criterion and correctness of this analysis is verified by com-puter simulation.