Abstract: The Nb segregation regulation and behavior in liquid phase were calculated using a thermodynamic calculation method and corresponding Ni-base database for two Nb-rich superalloys. The calculated results are agreeable with experimental values from references. Based on this model, the Nb segregation degree and the maximum Nb segregation content in liquid-solid temperature range do not linearly increase with increasing Nb content, but rising to the maximum then droping. However, the Nb segregation degree monotonously increases with increasing liquid-solid temperature range. According to this theoretic calculation, a method for alloy design was discussed in term of reducing Nb segregation and enlarging ingots.