Abstract: This paper analyzes the characteristics of the planar antenna with multiple subarrays, which indicates that the sidelobe of the antenna is difficult to reduce by the perturbation of amplitude weighting. In order to reduce the maximum sidelobe level of the antenna in the whole elevation scan range, the subarray distances are optimized by genetic algorithm (GA), and then the effects of antenna element directivity and amplitude perturbation on sidelobe suppression are discussed. Simulation results prove the validity of the theoretical analysis, and show that the optimization subarray distances can suppress the sidelobe level effectively, especially when the number of subarray is large under the same antenna aperture. The methods and results can be used as reference to the design of the planar antenna with multiple subarrays.