A accelerated arithmetic algorithm of the dynamic computing regions was designed, and 3-dimensional numerical simulation of isothermal solidification for a binary alloy was implemented. The dendritic growth and the recalescence of Ni-Cu binary alloy during the solidification at different cooling rates were investigated. The effects of cooling rate on dendritic patterns and microsegregation patterns were studied. The computed results indicate that, with the increment of the cooling rate, the dendritic growth velocity increases, both the main branch and side-branches become slender, the secondary dendrite arm spacing becomes smaller, the inadequate solute diffusion in solid aggravates, and the severity of microsegregation ahead of interface aggravates. At a higher cooling rate, the binary alloy presents recalescence; while the cooling rate is small, no recalescence occurs.