In this study, an optimization method for the orientation arrangement of antenna-array elements to achieve high gain and low sidelobe levels (SLL) based on weight coefficient regulation, is proposed. In the method, the fitness function is defined as the weighted sum of the maximum gain and the difference between the maximum gain and SLL. By introducing an appropriate weight coefficient, the design requirements of the antenna-arrays for high gain and low SLL are realized. The optimization results under different weight coefficients are discussed, and the radiation patterns are synthesized and summarized based on these coefficients. The full-wave method of moments(MoM) is adopted to adequately consider the coupling field of each array element. The optimization problem is solved via a genetic algorithm (GA), and two typical examples, including linear and planar dipole antennas, are presented. The results show that when weight coefficients of 0.45 and 0.9 are used, the established optimization method significantly reduces SLL and cross-polarization gain, while ensuring that the main beam gain in the desired direction is maintained. Thus, the results verify the effectiveness of the proposed method.