Abstract: Taking aerospace precision instruments as the typical application scenario, with ultra-high modulus and low expansion coefficient as the research and development goals, the particle size distribution design for ultra-high volume fraction SiC_P/Al composite materials was designed and the performance was optimized. The influence of coarse particle size in particle gradation on the mechanical properties and linear expansion coefficient of the composites with different volume fraction silicon carbide (SiC) was systematically investigated by double-particle gradation method and mechanical powder mixing process. The results show that with the increase of SiC particle volume fraction, the linear expansion coefficient for all the composites monotonically decreases. When the volume fraction is 70%, increasing the coarse SiC particle size can further reduce the linear expansion coefficient. When the coarse particle size is greater than 100 µm, the flexural strength of the SiC_P/Al composites with 70% volume fraction decreases somewhat, but the flexural modulus and micro-yield strength are superior to those of the composites with 65% volume fraction, demonstrating the ideal comprehensive performance. When the coarse particle size is less than 100 µm (73 µm), due to the overly narrow spacing between coarse particles, the fine particles agglomerate, and the relative density decreases, the mechanical properties of the composites with 70% volume fraction are inferior to those of the samples with 67% volume fraction. In the final determined optimal formula, the mass ratio of 123 µm to 11 µm silicon carbide particles is 3:1, and the volume fraction is 70%, the corresponding flexural strength of the composites is 379.61 MPa, the flexural modulus is 264.34 GPa, and the coefficient of linear expansion is 7.10×10^‒6 K^‒1.