A numerical analysis was carried out for the negative pressure development in a solidifying Al-Si binary alloy ingot. In the analysis, the both effects of interdendritic fluid flow and solid deformation due to solidification shrinkage were taken into account. The developed negative pressure causes the formation of micro-pores. In order to confirm the validity of the analysis, the calculated negative pressure distribution was compared with the density distribution in a solidified ingot. When only the effect of interdendritic fluid flow is considered, the calculated negative pressure shows the maximum value of -26MPa. On the other hand, by considering both effects of the liquid flow and the solid deformation, the increase in the negative pressure is restricted to the maximum value of about -0.7MPa because the negative pressure is accommodated by solid deformation. The density distribution in the solidified ingot agreed with the calculated negative pressure distribution.