A steady-state non-equilibrium dendrite growth model was extended for binary alloy assuming non-linear liquidus and solidus. Satisfactory agreement of the model prediction with the experimental data of Ni-0.7at.%B and Ni30Cu70 alloys was achieved. The velocity plateau as experimentally observed in the velocity versus undercooling is quantitatively analyzed in terms of this model. Accordingly, the initiating point (i.e. corresponding to the critical velocity of absolute solutal stability VC*) and the ending point (i.e. corresponding to the velocity of maximal tip radius VRm) of the plateau are characterized.