The influence of squeeze casting pressure on nanoparticle distribution and mechanical properties of 2 wt.% nano-SiC_p/Al-Cu composites assisted with ultrasonic vibration was investigated. Results show that as the applied pressure increases from 0 to 400 MPa, the α(Al) grains are significantly refined at first and then the refinement trend slows down, and the porosity of composites is gradually reduced. When the applied pressure is 400 MPa, α(Al) grain size is reduced from 105 to 25 μm, and the nanoparticle distribution is significantly improved, resulting in the optimal mechanical properties of the composites. The ultimate tensile strength, yield strength and elongation of the composites are 290 MPa, 182 MPa and 10%, which are 52.6%, 25.5% and 400% higher than those of the nano-SiC_p/Al-Cu composites prepared by gravity casting (0 MPa). The enhancement in strength and elongation of nano-SiC_p/Al-Cu composites under high pressure is mainly attributed to grain refinement, reduction of porosity and uniform distribution of nanoparticles.