The sidelobes of the planar antenna with multiple subarrays (MSPA) are caused due to its dispersed aperture.This paper analyzes the factors of peak sidelobes level forming for the antenna at different elevation angles and proposes some suppression methods.In order to reduce the peak sidelobe level of the MSPA in the working range the effect of the antenna aperture element directivity and amplitude attenuation are studied by using genetic algorithm and the peak sidelobe optimization is realized.The simulation results show that the integration of the MSPA orientation diagram needs only to consider the minimum subarray spacing constraint.Furthermore the element directivity and amplitude attenuation should be also taken into account in the optimization process.The methods and results can be used as a reference to the MSPA design.