Problems of dynamics of rectifying column modelling were shown. The solution of the problem of extensive time consuming computation of transient states was searched for, Mathematical model of distillation column was reduced using Lagrange polynomial in the interpolation way assuming continuity of the column's section's profiles. Increase of the accuracy was realized on the basis of interpolation theory using Lebesque function. The results of the computations from classical and reduced model were verified using own and literature experimental data.