HXI (Hard X-ray Imager), one of the three main payloads of the ASO-S (Advanced Space-based Solar Observatory) satellite, is a Fourier-synthesis imager.It uses 91 sets of grid sub-collimators arranged at different angles and pitches to obtain 45 space-modulated Fourier transform pairs, and to reconstruct the hard X-ray (30--200keV) images of the solar flare sources, and the resolution can reach as high as 3.1'. On the premise that grids pitch are determined, the arrangement of the grids can still affect the imaging quality. In this paper, the optimal distribution of the grid placement is obtained by analyzing the relationship between the instrument's mu\nu distribution of the Fourier components and the corresponding evolution of the point spread function. This result will be used as the basis for improving HXI instrument design and developing scientific analysis software.